History and Archeology of Urban Decline: Rome during the Medieval Climate Anomaly

Periodization of Decline and Revival in Medieval Rome

Until recently, the prevailing historiographical approach generally defined the period between the fall of Rome in the fifth century and the later Middle Ages, as a period of decline, with spells of urban revival. This approach owes much to Richard Krautheimer’s monumental Rome—Profile of a City, 312-1308. Krautheimer noted two such periods of revival, namely, the so-called Carolingian (i.e. ninth century) and twelfth-century Renaissances, which he interpreted as manifestations of the contemporaneous rise in the political power of the papacy. ⁵ His account also preserved an image of a city whose diminished population settled in the abitato, concentrated around the Tiber bend and covering only a portion of Rome’s former area, with the rest of the city falling into a ruinous condition, and eventually forming the ruralized disabitato. ⁶ This spatial division persisted throughout the Middle Ages, albeit with shifts in the proportion between the two areas over time.

Both urban revival and decline were assessed through the viewpoint of monumental and religious architecture, which was most commonly sponsored by the papacy. ⁷ Within this framework, the eleventh century is perceived as a transition period between the urban revivals of the ninth and twelfth centuries and is defined by such watershed moments as the Norman sack of 1084, or the events of the Gregorian reform. ⁸ The perception of the eleventh century as an in-between period in the city’s history is further reinforced by archeological accounts, which often focus either on early medieval (sixth-tenth centuries) or on late medieval (twelfth-fifteenth centuries) sites and findings. Indeed, very few Roman edifices can be dated to the eleventh century, while instead, as we shall see, some areas of the city which were previously inhabited present evidence of abandonment during this period. ⁹

Yet recent scholarship is increasingly critical of such strictly geo-political interpretations of the history of medieval Rome and the extensive archeological and historical studies conducted over the past decades have continuously challenged this traditional narrative. ¹⁰ Thus, Hendrik Dey and Étienne Hubert convincingly challenged the divide between abitato and disabitato, promoting instead an image of the cityscape that Dey has dubbed the “leopard-skin” pattern. This term encapsulates the uneven character of the urban fabric that alternated between densely populated areas and stretches of land occupied by ruins, orchards and pastures. ¹¹ Chris Wickham questioned previous axioms concerning medieval Rome and framed the century between 1050 and 1150 as a period of crisis that stemmed from a refashioning of Roman social and governmental structures. In doing so, he advanced an alternative socio-economic and political interpretation of urban development in Rome during this period. ¹² Other, more specifically focused studies, such as Louis Hamilton’s re-evaluation of the impact of the Norman sack of 1084, further challenged some of the prevalent premises concerning Medieval Rome. The latter has convincingly argued that the impact of the sack on the cityscape was much more limited than previously thought, and was limited to very specific areas of the city, one of them being the Celio. ¹³

Despite their departure from former narratives, most of the revisionist studies still support the traditional periodization that views the tenth and eleventh centuries as one temporal unit, conditioned mainly by socio-political events, thus retaining their role as key factors in our understanding of urban development during this period. However, an analysis of changing climate conditions in the medieval Mediterranean may provide us with a complementary explanation for some of the changes in the urban fabric of eleventh-century Rome.

Climatic Crisis, Water Supply, and Archeology of Abandonment. An Alternative Prism for the Analysis of Urban Decline in the Eleventh-Century Rome

Recent studies of the implications of the medieval climate anomaly (hereafter MCA) reflected a difference between the Eastern and Western Mediterranean. ¹⁴ Although it is difficult to conclusively determine the causal connections between these different climate conditions and concomitant changes in human society, it has been suggested that while the east suffered a series of calamitous events, the west experienced improved climatic conditions. ¹⁵

Analysis of the effects that these crises had on the cities of the Eastern Mediterranean clearly shows the importance of the external provision of fresh water to the wellbeing, growth, and even survival of cities. ¹⁶ According to modern measurements, a decade-long decrease in the amount of rainfall can lead to a significant decrease in agricultural output and result in the drying up of springs and the consequent ruin and abandonment of waterways. ¹⁷ Furthermore, it is argued that aqueducts providing running water enabled urban growth in the Mediterranean climate, provided food security, and affected the high standard of living and affluence of their citizens. ¹⁸ The opposite is also true, as the destruction or abandonment of aqueducts and other water infrastructures could lead to demographic decline and greatly affect the standard of living of those who remain.

Well-documented cities known for their water-supply systems afford a unique opportunity to study these processes and to establish a more nuanced understanding of the connection between the provision of fresh water and urban development. Thus, an examination of cities such as Jerusalem and Fustat during the MCA points to a correlation between the decrease and finally cessation of water supply from outside the city, or in the case of Fustat, the decline of the height of the Nile inundation and a significant decrease in the population and consequently considerable shifts in the urban layout. In Jerusalem, the demographic shift that entailed its physical contraction led to changes in the outline of the city walls that were rebuilt on a reduced scale. Similarly, in Fustat, the neighborhoods that were abandoned in the eleventh century were not rebuilt until the late twentieth century. ¹⁹

Its location between two climatic regions that were differentially affected by the MCA, combined with its rich documentation, and elaborate systems of water supply, make Rome a particularly appealing case for studying the impact of the climatic change of the eleventh century. ²⁰

Studies of climate conditions in Italy suggest that the southern and northern parts of the peninsula were affected by different climate conditions, roughly corresponding with the east-west division of climate regions in the Mediterranean during the MCA. Situated in the center of Italy, Rome marks the junction between these differently affected climatic regions. ²¹

Indeed, it is more difficult to conclusively interpret paleoclimatic evidence for this region, than for such regions as the Southern Levant, or more western regions of Europe during the period in question. For example, despite studies that reconstruct arid conditions in Sicily and some regions of Southern Italy before and during the eleventh century, simultaneously there is evidence of continuous agricultural activity in the same regions. ²²

The effort to resolve some of this seemingly contradicting data, and to incorporate it into a coherent narrative that would link climate change and historical processes, reflects one of the fundamental challenges of studying past climates, namely, the establishment of causal relations between climate and societal change. In the abovementioned case, regional paleoclimatic patterns were associated with large-scale geo-political shifts such as the changing nature of Byzantine rule on the island and additional regions in Southern Italy, the Muslim conquest of Sicily, and the Norman conquest later on. However, as recent developments in the field show, it is necessary to develop more nuanced and region-sensitive frameworks that would emphasize human agency and adaptation of socio-economic structures to changing climate condition. ²³

Thus, while recent studies increasingly corroborate the notion of a climatic east-west division of the Mediterranean basin, and occasionally the Italian peninsula is indeed counted among its eastern regions, it nevertheless was not unequivocally placed on one side or the other. ²⁴ A more regionally nuanced approach that is applied in another recent study sheds new light on this issue. This study traces positive climate conditions associated with the MCA in northern Italy and negative conditions in the south of the peninsula, an issue we shall return to later. ²⁵

Yet geographical location alone cannot account for the implications of the MCA on urban growth or decline, especially when these are examined through the prism of water supply and water infrastructures. First, as studies show, evidence concerning medieval climate change in this borderline region is often inconclusive, and second, an analysis of their impact on settlement patterns calls for a consideration of human agency and adaptation to changing climate conditions. ²⁶

The latter point is particularly important in the context of water supply in cities with such elaborate water infrastructures as Rome. As Dora Crouch had shown in her study of water management in ancient urban environments, cities never relied solely on their aqueduct systems, no matter how elaborate they were. To mitigate such risks as maintenance costs, contamination, or changing environmental conditions, cities relied on diverse water sources (such as cisterns, springs or rivers). ²⁷ Thus, the failure of a certain water infrastructure would not necessarily lead to full-scale deterioration, but rather to adaptation through changing settlement patterns, or intervention that would divert water from another source. As we shall argue in the following passages, urban development in Rome during the eleventh century is a particularly interesting case in point, as its extensive documentation allows us to trace the connection between an interruption of water supply to the Celio and changing settlement patterns in the city.

The Celio in Imperial and Late Antique Rome

The history of the Celio is closely tied to the history of the water supply to Rome and particularly to the construction of the Neronian extension of the Aqua Claudia and the various monuments and installations depending on the provision of fresh water ²⁸ (Image 1). This extension led to a considerable development of the Celio and a process of urbanization and densification of both public and residential areas, as well as other urban infrastructures, especially on the northwestern side of the hill. ²⁹ These developments were prompted by the construction of a monumental reservoir (“castellum”) providing water to both the aqueduct branch leading to the Palatine and to the Stagnum Neronis (“Nero’s lake”) where the Colosseum was later built. Colini and other scholars even suggested that the castellum and other dependent water distribution infrastructures enabled the construction of the Domus Aurea on the adjacent hill. ³⁰

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Image 1.

Neronian extension of the Aqua Claudia.

Thanks to this monumental reservoir, the Celio became replete with multiple public and private water infrastructures, including smaller reservoirs, nymphaea, latrines, and so on (Image 2). ³¹ The abundance of running water also prompted the construction of private edifices that catered mostly to the Roman nobility. ³² Although an exhaustive examination of the history of the Celio is beyond the scope of this study, several examples that demonstrate the importance of the water supply to the development of this area over time are in order.

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Image 2.

Fresco at the nymphaeum on the Celio.

The thoroughly excavated elaborate Roman domestic complex along the Clivus Scauri, one of the ancient roads crossing the Celio (Map 1-IV), illustrates the intensification of late Roman settlement in this part of the city. ³³ With the increasing Christianization of the cityscape of late antique Rome, the edifices on the Celio were either transformed into Christian residences, as were the houses on the Clivus Scauri, or served as domestic complexes on a reduced scale. ³⁴ This process continued into the Middle Ages with the construction of new churches on pre-existing Roman foundations, as was the case with the Basilica of SS. Giovanni e Paolo, S. Stefano Rotondo, and other churches in this area. Many of these endeavors were associated with papal endowments and patronage and were not restricted only to churches. ³⁵ Such evidence indicates that the area continued to be rather densely populated during this period as well.

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Map 1.

The Celio.

The Celio between the Early and Central Middle Ages

The Aqua Claudia continued operating and supplying the area of the Celio with fresh water throughout the early Middle Ages and was even included in papal renovation endeavors, for example, during the papacy of Hadrian I (772-795). ³⁶ This continuity was ascribed to the strategic importance of supplying water to the Lateran. ³⁷ Nevertheless, as we shall see, there is evidence suggesting that the Aqua Claudia ceased to function by the early eleventh century.

Churches on the Celio were included in the extensive renovations of the ninth century. S. Maria in Domnica, also known as “alla Navicella,” was rebuilt by Pope Paschal I, and the importance of the adjacent basilica of SS. Giovanni e Paolo was growing at the same time. ³⁸ Furthermore, the status of S. Maria in Domnica as a diaconia (a welfare institution), provides further support to the notion of the continuation of settlement on the Celio during this period, as such centers were usually found in well-populated areas. ³⁹

Interestingly, some of the monuments established on the Celio during this period retained toponyms related to water and its symbolic importance. For example, while “alla Navicella” is a much later toponym related to the fountain placed at the entrance to the church, it may have also echoed the memory of a temple dedicated to Isis as protectress of sailors, which was transformed into an early Christian church. ⁴⁰ Another case is that of S. Tommaso in Formis, a monastery founded probably around 1000, located—as suggested by its name—directly beneath the branch of the Aqua Claudia along the northwestern side of the hill (Map 1-V). ⁴¹

The rich documentation that has survived from religious institutions in Rome and its environs allows us to partially reconstruct the distribution of properties around the Celio. Documents from the Regesto Sublacense provide evidence for settlement on the Celio during the tenth century and clearly show that the hill was supplied by the still active Aqua Claudia. ⁴² The monastery of S. Subiaco was united in 938 with the monastery of S. Erasmo on the Celio, whose cartulary preserves many documents concerning this area. Based on this documentation, it is possible to partially trace the development of several settled areas along the course of the Aqua Claudia both within and outside the city walls. One such inhabited area was located near the Porta Maggiore, where the Aqua Claudia entered the city walls, and another in the vicinity of the monastery of S. Erasmo on the Celio. ⁴³ Several documents, mainly from the tenth century, attest to the settlement in these areas, often using the aqueduct as a landmark delineating the properties that were exchanged, some of them clearly testifying that it still functioned. ⁴⁴

By the tenth century, settlement patterns on the Celio seem to have been similar to those observed by Hubert in other, more peripheral areas of the city, namely, the hills surrounding the Campo Marzio. ⁴⁵ These patterns consisted of a more ruralized form of settlement, with hamlets adjacent to different monuments such as aqueducts, walls, gates, and Roman monuments, yet nevertheless formed a continuum with the settled areas close to the “core” of the city near the Tiber bend. ⁴⁶

However, the evidence concerning the eleventh century reflects a significant shift and also provides us with a terminus ante quem concerning the functioning of the aqueduct. ⁴⁷ Thus, the last mention of the aqueduct is in 1006, when the document explicitly refers to a “[. . .] canale qui mittit aqua de forma, a secondo latere forma Claudia [. . .],” ⁴⁸ suggesting that at that time the aqueduct still operated. Such formulations cannot be found in any of the later documents. This coincides with the decline in references to the settlement in the surroundings of the aqueduct, indicating a process of abandonment or dwindling of the previously populated area.

Several additional documents, preserved in the archives of SS. Andrea e Gregorio in Clivo Scauro on the Celio, may provide further evidence of similar processes of decline. From 975, the monastery was engaged in the development of areas on the slopes of the Celio toward the Circus Maximus and the Aventine. ⁴⁹ However, the monastery’s involvement in this area ceased in 1025 for more than a century and was renewed only in 1145. ⁵⁰

Further evidence for the decline of water supply and subsequently—of the urban fabric in the Celio, can be found with regard to S. Tommaso in Formis. Although, as mentioned earlier, a monastery probably existed there already around 1000, there are no documents attesting to it from the eleventh century, with systematic records renewed only toward the thirteenth century, when the monastery became the headquarters of the Trinitarian order. ⁵¹

Additional evidence sheds more light on the connection between the monastery complex and water infrastructures in its vicinity. A later map reconstructing the complex shows a piscina limaria, that is, a cistern used for water purification prior to its distribution, which was an integral and probably an original part of the Roman aqueduct system that was adjacent to the church. By the time the complex was taken over by the Trinitarian order in the thirteenth century, the aqueduct no longer operated, and the former reservoir was already used as a cellar. ⁵²

A final point to be considered in regard to the water supply to the Celio during the central Middle Ages, is its proximity to the Lateran, which, as pointed out earlier, also depended on the Aqua Claudia. Although we may not possess direct evidence concerning water supply via the aqueduct to the Lateran complex during the eleventh century, Hendrik Dey has recently suggested that the construction of a canal under Pope Calixtus II (1119-1124) in order to divert water to the Lateran, was prompted by the failure of the aqua Claudia during the preceding century. ⁵³

This brief excursus suggests that the aqueduct on the Celio, and some of its dependent water infrastructures, continued to function, at least on some level, throughout the early Middle Ages, and until ca. 1006, affecting the urban fabric in this area. However, from the beginning of the eleventh century, various evidence suggest a process of abandonment and decline. Thus, several settlement clusters that are attested in the archives of SS. Andrea e Gregorio before the eleventh century, including those around Porta Maggiore and S. Erasmo, and on the slopes of the Celio, are no longer mentioned in any of the documents from the eleventh century. Similarly, evidence concerning S. Tommaso in Formis, suggest that the monastery and its water-related infrastructures were abandoned shortly after its foundation during the eleventh century, and re-occupied (or repurposed, as in the case of the piscina limaria) only toward the beginning of the thirteenth century. Such evidence stresses the connection between the continuity of settlement in the Celio and stable water supply, which when interrupted would have led to the decline of this part of the city.

Examined within the broader methodological framework mentioned earlier in this article, the evidence from the Celio raises several observations concerning the connection between urban growth or decline and archeology of water supply. As demonstrated in our discussion of the Celio during the imperial and late antique periods, the settlement of this area reflected the city’s expansion during periods of wealth, precipitated by the construction of infrastructures securing abundant water supply. While interruption of this supply resulted in the decline of the Celio, this does not imply that other areas of the city were similarly affected. The archeological evidence shows that areas such as the Tiber bend and the forum became more densely populated. ⁵⁴

Combined with evidence from the Celio, this attests to the shrinking of the settled area of the city and its concentration around the river, concomitantly with the abandonment of more peripheral regions that relied on external water supply. ⁵⁵ In other words, the impact of water supply on urban growth or decline is not linear or uniform, but rather is reflected in changing settlement patterns, namely, the abandonment or ruralization of certain areas, and the densification of others, as a form of adaptation to changing conditions.

Climate Crisis and the City of Rome in the Eleventh Century

Closer scrutiny of some of the sources referring to the Norman sack of Rome provides additional clues concerning the conditions around Rome during the period in question, suggesting that the entire region was affected by climatic anomalies (droughts or very cold winters) and their societal consequences. These sources refer to food shortages in Southern and central Italy, usually associated in these regions with dry spells, which occasionally led to famine and riots.

Alongside the complex geo-political factors that were at play in facilitating the advance of the Normans in Southern Italy, recent studies proposed a complementary explanation, focusing on climate change during the MCA. This line of argumentation posits that economic deterioration in the Eastern Mediterranean, which resulted from repeated droughts and cold anomalies during the eleventh century, allowed the Normans to benefit from the subsequent instability and to gain a foothold in Southern Italy. ⁵⁶ While proxy-based studies of the climate conditions in these regions mainly refer to drier weather and reduced precipitation, the historical evidence provides a more nuanced picture. Such accounts suggest a connection between climate conditions and negative societal implications, similar to those described in the Eastern Mediterranean. ⁵⁷

As Thomas Wozniak has recently argued in his extensive study of medieval accounts of natural disasters, these were often employed as literary topoi that facilitated religious or political reasoning for certain events. ⁵⁸ While this observation surely calls for a cautious reading of these accounts, their analysis, together with some of the abovementioned proxy-based studies of climate conditions in the Medieval Eastern Mediterranean as well as texts from other genres, yields a more complete picture of the societal implications of climate change in this region. These suggest a connection between climatic factors and episodes of tribulations and instability in Southern and Central Italy and Sicily, which can be attributed to a “ripple effect” of the crises that impacted the Eastern Mediterranean during the same period. ⁵⁹ Although a comprehensive analysis of all extant evidence concerning this issue merits an independent study, even a preliminary survey provides an accumulation of references to harsh climate conditions, found in various types of sources that range from letters from the Cairo Geniza to Norman chronicles.

The earliest of these accounts begin to appear in the first years of the eleventh century in the annals of Southern Italy. Thus, the Annales Barenses reports heavy snowfall in 1009, which destroyed olive trees and killed fish and birds. In May that year, a rebellion occurred, and in August, the city of Cosenza in Calabria was taken by the Saracens. ⁶⁰ A similar account appears in the Annales Beneventani, which also mentions a heavy drought that lasted for three months, just three years earlier. ⁶¹

Although writing several decades later, in the 1090s, William of Apulia reports additional instances of similar anomalies that prompted tax revolts in Southern Italy between 1017 and 1020. According to his account, the first rebellion of the Normans in Apulia against the Byzantine overlords in 1017 was preceded by an unexpected and unprecedented severe cold spell:

At this time the Italians were astounded by the fall of an extraordinary and up to then unprecedented quantity of snow, which killed the bulk of the wild animals and cut down trees, never to grow again. ⁶²

The small number of Norman rebels participating in the uprising (between 300 and 2,500) emphasizes the fragility of the Byzantine government during periods of dearth. ⁶³ The cold spell that affected the southernmost Italian provinces, may have lasted well into the 1020s or perhaps even later, as suggested by another entry in the Annales Barenses for the year 1024. Moreover, it could have been the catalyst for new taxes and the violent tax revolts that broke out in the Sicilian countryside from 1019 to 1020. ⁶⁴ The imposition of new taxes on grain, fruit, and vegetables resulted in the siege laid by the people of Palermo to the castle of the Muslim governor. ⁶⁵ New taxes in Sicily are also attested in a letter from the Cairo Geniza, reporting taxes levied from the Jewish community sometime before 1020, prompting many of its members to immigrate from the island. ⁶⁶

Another cluster of calamitous events can be observed in the 1050s. Several letters from the Geniza report the dire conditions in Sicily at the time that caused many to flee the island. ⁶⁷ Particularly telling is a letter from 1053, in which the author refers to information he received from the Jewish residents of Mazara del Vallo, who report that

[. . . ] he who had anything went away, and he who had something belonging to someone else consumed it. Even a case of cannibalism has been reported. [. . .] 23 families left for Mahadia, including their men, destitute and naked. ⁶⁸

While such evidence may be ascribed to the political turmoil on the island during those decades, an account composed by Goffredo Malaterra, referring to Calabria in the spring of 1058, suggests a connection between environmental factors and the dire conditions in the entire region:

In the year 1058 there was a great disaster [. . .] [that] afflicted the entire province of Calabria for three months—that is, March, April and May. [. . . ] First [. . .] the raging sword of the Normans spared virtually no one. . . . Second was the famine that consumed the weak. [. . .] Third was the stroke of disease that, spreading horribly, permitted virtually no one to escape untouched. [[. . .] Even those who had money had nothing to spend it on. Some [. . .] sold their very children into slavery for a trifle, then when they tried to spend it on something that they could use for food they found nothing to buy. [. . .] dysentery, [[. . .] proved deadly to many; others it rendered splenetic. [[. . .] The sterility of the land took away the fresh greens that they were accustomed to using for food. When they were found and eaten, they seemed to do more harm than good, withered as they were by a certain hoarfrost in the pestilential air. The people tried to make bread out of river grass, and the bark of certain trees, along with chestnuts, and the nuts of Italian oaks and holm oaks called glandes [acorns], which they took from the pigs, dried, ground into meal, and mixed with a little millet. [. . . Mothers, moved by pity, were reduced to a kind of shameless violence, snatching such food from the mouths of their own children rather than administering it to them. ⁶⁹

Additional evidence indicates that such calamities were affecting the entire region at the time. Thus, Geniza letters that report on the difficult conditions in Qayrawān further attest to the abovementioned boundaries between different climate regions in the Eastern and Western Mediterranean at that time, showing the effect of the crisis on the North African coast. Two of them, dating to 1056, report dearth and food shortages, as well as an epidemic. ⁷⁰

A final cluster of evidence appears in some of the accounts of the sack of Rome in 1084 and refers to hunger in and around the city in that year. The famine and harsh weather are mentioned in two independent sources. The closing sentences of the account of the events of 1084 as described in the Liber Pontificalis, entries in which were resumed in the beginning of the twelfth century, after centuries of hiatus, read: ⁷¹

In that year there was a great famine throughout the world, after which many people died. And there was a solar eclipse, the earth shook, and the castle of S. Angelo was taken. ⁷²

A combination of three natural disasters, such as hunger, solar eclipse, and earthquakes, occurring simultaneously, is a well-known medieval topos and should not be taken at face value. Nevertheless, additional evidence concerning the same events shows that this text may have a kernel of truth. ⁷³ A short quote, describing mass casualties that the chronicler himself associates with weather conditions, supports the description in the Liber Pontificalis. Thus, The life of Henry IV, written probably shortly after 1106, refers to a sickness that afflicted the entire imperial garrison stationed in Rome in 1083. The sickness referred to in this passage was in high probability malaria, epidemics of which were known to have occurred in medieval Italy in correlation with changing climate conditions. ⁷⁴ As shown in recent studies pertaining both to present and to past climate conditions, such seasonal outbreaks of disease, malaria among them, can often be connected to changing eco-systems as a result of climate change. ⁷⁵

Although this account takes a much more restrained tone, it may nevertheless corroborate, at least partially, our claim that the dearth and hardships described in these passages were caused by the climatic anomalies prevailing at the time in and around Rome:

Finally, when everything in Rome was set in order and a garrison had been established in the City, lest she [Rome] alter her state of fidelity, the Emperor, functioning in the height of his new dignity, went back into the German Kingdom. But no fortune lasts long; for those whom the Emperor had established as garrison in Rome were seized in sickness which both the place and the season produced—for it was summer—and died without even one survivor. ⁷⁶

In this case too, additional evidence attests to weather anomalies affecting the Eastern Mediterranean in the 1080s. Thus, William of Apulia describes a particularly harsh winter in eastern Greece ca. 1081:

An unusually cold winter led the people quartered near the river Glykys to sicken. A great many of them suffered from cold and hunger, and disease spread so rapidly that almost ten thousand men died in less than three months. Nor did the rest of the army escape this deadly peril. In a very short period disease killed five hundred knights; and a large number of the common people also died. Neither knight nor sailor nor anybody else could avoid death striking them down. ⁷⁷

Conclusion

This study suggests that the urban fabric of the Celio, one of Rome’s seven hills which retained its urban prominence well into the early Middle Ages, underwent a process of decline during the eleventh century. We further argue that the fate of the Celio in this period should be seen within a broader context of the transitional eleventh century in Rome at large. Our analysis aimed to show that processes of decline were nuanced across the cityscape. Thus, due to increasing reliance on the Tiber for water supply, the settlement on the Celio dwindled or became more dispersed, while areas closer to the river bend became more densely settled.

Unlike conquests or spectacular battles, episodes of deterioration are not necessarily singular events. They are difficult to piece together from the written sources, do not leave distinctive material traces, and often present contradictory, or unevenly spatially distributed, evidence. Thus, the densification of settlement in the Campo Marzio or the Forum, hitherto interpreted as a marker of urban growth, can be seen in a different light when examined vis-à-vis other areas of Rome, such as the Celio. These difficulties often lead to a disproportionate emphasis on geo-political factors or crises as primary causes of urban decay.

The present study offers a possible method of tracing these elusive processes: we focus on the Celio, a specific area of the city, located in proximity to the center of Rome. The importance of the Celio stems not only from its location but also from the edifices constructed there already in the first century CE, alongside the aqueduct that crossed the hill and provided water to the Palatine and to Nero’s Lake. Throughout Late Antiquity and the early Middle Ages, the settlement on the Celio relied on external water supply, as can be gleaned from the water installations recorded there, toponyms, and decorative art preserved in this area. Our choice to focus on the Celio relied not only on these factors but also on the wealth of archeological and textual evidence from the examined period, which refer to monastic properties, hamlets, and other infrastructures located in this area during the Middle Ages.

This wealth of well-dated information already led scholars to conclude that the water supply to the Celio did not stop in the sixth century as a result of the Barbarian invasions, and that water continued running in the Neronian branch of the Aqua Claudia until ca. 1006. However, the beginning of the eleventh century marked a turning point, ushering in a period of decline during which new construction works came to a halt, to be renewed only in the mid-twelfth century, water infrastructures ceased to function or were repurposed, and the entire area significantly dwindled.

We propose that the timing of this partial abandonment, and the cessation of the functioning of the aqueduct supplying water to the Celio, can be seen in correlation with the early phase of the MCA, when the Eastern Mediterranean was affected by a series of climatic crises, with far-reaching socio-economic implications. The crises in the east began with cold spells and extended droughts that decreased the amount of food and fresh water, causing, among other things, the deterioration of cities that depended on external water supply. At the same time, the western Mediterranean enjoyed a period of relative stability and even flourished. The location of Rome on the border between these two climatic regions and the historical importance of external water supply for the thriving of its urban fabric make it a particularly interesting case study for the examination of the effects of such climatic fluctuations in the eleventh century.

In the final part of our study, we suggest that the reasons for the abandonment of the Aqua Claudia and the discontinuation of water supply to the Celio can be traced to the harsh climatic conditions in Southern and Central Italy during this period. Our conclusions indicate that the Celio suffered considerable decline prior to the Norman sack, previously thought to have had a considerable effect specifically on this area of the city.

This emphasis on the climatic history of Rome aims to break away from traditional strictly socio-economic and political analyses of Roman urban development. Thus, while most histories of the city in the eleventh century analyze its vicissitudes in the context of the papal-imperial conflict, we offer an alternative approach, introducing climate conditions as a new factor to be reckoned with. This approach yields several interesting methodological assertions, as well as specific observations relating to the history and historiography of Rome.

From the methodological standpoint, we contend that the study of the decline of urban fabric should be based on richly documented and well-defined areas, with well-dated evidence. A focus on case studies that meet such criteria would allow reconstructing processes over time, unlike case studies that—due to the type of extant documentation and geographical scope—draw our attention to singular events. Moreover, we argue that while most studies of the archeology of water systems tend to focus on their establishment and development, the study of their decline is equally important.

Another set of inroads to future inquiry concerns the history and historiography of Rome, in the context of the MCA. For example, the location of Rome at the intersection of two different climate regions raises questions concerning the spread and the impact of climatic phenomena. Thus, there are differences in the impact of the crisis of the Eastern Mediterranean across different regions. While cities located at the epicenter of the climatic phenomena associated with the crisis, such as Baghdad and Fustat, suffered an overall rapid decline, the evidence concerning Rome, located at the periphery of the affected region, is less conclusive. ⁷⁸ Although some areas in the city, such as the Celio, declined, this was not necessarily an all-encompassing process that affected the entire city in the same measure. This suggests a “ripple effect” that determines the severity of the impact of the climatic crisis depending on the distance from its epicenter. We hope to have shown that to corroborate this assumption, a systematic analysis integrating historic and scientific proxies is valuable.