Adapting to a changing landscape & escalating floods

Lacking a modern awareness of geological processes, the early inhabitants of Rome were unable to predict how their investments in urban infrastructure and deforestation could cause reverberating environmental consequences. Nor could they foresee how the patterns of Tiber floods would change over time, so that the adaptive efforts of one generation proved to be insufficient sometimes even in a matter of a few decades. While the Romans responded in a variety of ways over the centuries, their actions focused on accepting the inevitability of flooding and mitigating the effects of floodwaters, rather than attempting to prevent floods altogether.
The archaeological record shows that the Romans began to adjust their urban investments in the valleys by the late 6th century and would continue to do so over time. Although we lack a textual record until the 3rd century BCE to hear from the Romans themselves about the challenges they faced, the archaeological evidence speaks volumes: the early 6th century Temple of Fortuna, which had stood on the raised section of riverbank for only two or three generations, was abandoned, and in its place the Romans constructed a 6 m tall platform against the lower flank of the Capitoline Hill. This drastic response suggests that the Romans were adapting to novel flood threats. The renovation of the harbor sanctuary in the early 5th century—which required both the forfeiture of a divine structure and a sizeable investment of resources and manpower—established a new, artificial terrace that stood once again several meters above the river. On top of this large platform, the Romans once again aggrandized their riverbank with two new temple buildings (the ruins of which are still visible today at the archaeological zone around the Church of Sant’Omobono).
Photo credit:
Sant'Omobono Project
View of the archaeological zone around the Church of Sant'Omobono in Rome.
This enormous effort to lift structures away from floodwaters can be seen elsewhere, particularly the Forum Romanum, where a series of landfills progressively raised the ground level, presumably in response to floods of ever-increasing magnitude. With the notable exception of this sanctuary complex atop its artificial platform on the riverbank and the reclaimed land in the Forum Romanum, huge swaths of Rome’s lowlands were not urbanized for several centuries.
The process of building in a floodplain changes the ecology that leaves a discernible mark in the geoarchaeological record: once an area is paved, it is logical to expect that sediment deposited by floodwaters would be cleaned up, rather than left to accumulate over time. In the region of the Forum Boarium, coring survey shows that sediment continued to accumulate at least until the 3rd century BCE. We can infer, therefore, that even as the city of Rome grew significantly into the mid-Republican period—and even as Rome became the dominate force in Italy—the Romans continued to operate without significant physical investments in much of their river valley.
Another lowland area, the Campus Martius (the plain to the north of the Capitoline Hill which would also have been susceptible to flooding) was similarly used for seasonal activity that required minimal urban infrastructure. Whereas the Forum Boarium hosted commercial pursuits, the Campus Martius was originally exploited for military and athletic exercises. Only sporadic architectural features existed in the Campus Martius until Augustus made significant investments in the region in the early 1st century CE. By limiting the scale of urban development in lowland areas, therefore, the Romans could minimize the destructive consequences of flood events.
Eventually, however, the urban sprawl of Rome did stretch into the valleys in substantial ways and thus created new vulnerabilities. There is evidence that Romans began investing in embankment walls along the river as early as the 3rd century BCE, if not earlier. These structures, however, do not appear to have been aimed at preventing incursions from the Tiber. The available evidence of embankment walls at Rome throughout the ancient period suggest that they were low in certain areas and not the kind of cohesive line of high walls, which would be necessary to contain floodwaters. Instead, these walls served other important purposes: reinforcing the riverbank and shielding it from erosion, as well as providing mooring structures to secure boats. Atop these embankments, new architectural investments would define Rome’s riverscape: most notably, temple buildings resting on high podia, which would help them withstand floods. Even once the river valley was urbanized, the area would require regular maintenance. Among other activities, repeated dredging was necessary to clear the Tiber channel of debris and sediment, facilitating boat activity and creating accommodation space for flood waters. Flood events would have required clean up efforts to remove deposited silts as well as the periodic reconstruction of destroyed structures.
By the Late Republic, there came a formalized governmental response: bureaucratic offices, curatores alvei et riparum Tiberis or overseers of Tiber’s bed and banks, were created presumably in order to help manage the demands of riverbank maintenance and flood response.
With the advent of the historical record, we gain some deeper insight on the Romans’ discussions around the floods that beset their city. Even beyond efforts to manage and mitigate, it is worth noting that they also considered more radical efforts to control their volatile river.
For example, in the 1st century BCE, Julius Caesar made a proposal to modify the course of the Tiber by constructing an artificial canal that would divert the Tiber’s flow away from the city entirely.
Following a devastating flood in 15 CE, the emperor Tiberius appointed a special commission to address the issue. The Roman Senate debated various strategies, including engineering that would redirect or dam sections of the Tiber and its tributaries and control the amount of water outflow in the fluvial system. These aggressive measures, however, were ultimately not enacted.
It must be emphasized that by the late 1st millennium BCE the ancient Romans had the engineering capabilities to protect their city from floods, whether through the use of dams, artificial levees, canals, or other measures. Indeed, they pursued many large-scale landscape modification and hydrological control projects throughout their empire. The fact that they did not prevent floods in their capital was, therefore, at least partially a choice, not entirely an inevitability. There are numerous potential explanations for this seemingly irrational judgement, but three reasons should be highlighted.
  1. The Romans had an appreciation for the fact that rivers are complex systems: by obstructing or redirecting waters, risks would have been shifted to other communities in the region. Damming projects were ultimately discarded, in part because of the objections of other communities, which feared an increase in flooding or the loss of agricultural land.
  2. Technological innovations, particularly the invention of hydraulic concrete (which can set underwater and remain resilient in wet environments) in the late 2nd century BCE, significantly improved their ability to construct urban infrastructure in areas near the river. Indeed, the Romans eventually made major investments in port infrastructure along both banks of the Tiber, which ensured the importation of food stuffs and other goods necessary to support the city at its estimated peak of more than one million inhabitants.
  3. The Romans had religious reverence for the natural world. Many features of the landscape, including rivers, were seen to have divine essence. Rivers like the Tiber were often personified as gods, and natural disasters like floods were interpreted as omens from the gods. Overt efforts to alter the environment or control the river would therefore have religious connotations. The ancients’ veneration of the gods should be understood as another adaptive response that offered some sense of control over their situation: by appeasing the gods, they may look favorably on the city and withhold natural disasters.
Photo credit:
A.L. Brock
Photo of a neo-classical sculpture of Tiberinus (the Tiber River personified as a god) found today on the Capitoline Hill but based on ancient sculptures.
Continually susceptible to the Tiber’s fluctuations, Rome was affected by inundations and the devastating secondary effects of malaria well into the modern period. In the generation after Rome was made the capital of the newly unified nation of Italy in 1870, a series of significant floods submerged huge swaths of the city for several days. Photography at the turn of the century captured the adaptive capabilities of modern Romans, who boated around their city just as their prehistoric ancestors supposedly had.
Photo credit:
Ettore Roesler Franz
A watercolor painting from the Roma Sparita ('Vanished Rome') series, made by Ettore Roesler Franz between 1878-1896, depicting a flood in Rome.
Photo credit:
Baldomer Gili i Roig
Photograph taken near the Round Temple in the Forum Boarium during a flood in December 1900.
Faced with this recurring threat to his new capital, the Italian King, Vittorio Emanuele II, strove to modernize Rome and organized a commission to develop a plan to prevent such disasters. Officials explored a variety of strategies, including renewed discussion about rerouting the Tiber away from the city entirely. Ultimately, the decision was made to conduct a massive overhaul of the area along the Tiber River, which had been heavily encroached upon over the centuries. Buildings that lined the riverbank were demolished.
Photo credit:
Brizzi, B. (1989) Il Tevere. Un secolo di immagini.
Photograph of the Tiber River as viewed from the Aventine Hill in the mid-19th century.
Photo credit:
Ettore Roesler Franz
A watercolor painting from the Roma Sparita ('Vanished Rome') series, made by Ettore Roesler Franz between 1878-1896, depicting the urban construction that originally crowded the river bank.
By the completion of the project in 1910, the entire length of the river as it travelled through the city was encased in 40-foot high concrete walls. After the city had been afflicted by inundations for more than two millennia, this enormous urban renovation and investment in flood walls finally ensured that the lowlands of Rome would be protected from overbank flooding. Now, when the city experiences flooding, which is not entirely uncommon, this is often the unpleasant result of heavy rainfall and blockages in the city’s sewer system.
Photo credit:
Ewan Munro, Wikimedia Commons (CC BY-SA 2.0)
Photograph of the modern embankments of the Tiber River.
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