Text: Northern Autumn
Edited by Beiqiu
Core sampling in the Roman River Valley revealed a radical change in the landscape as the major cities grew in the early stages. After centuries of relatively stable and slow deposition. In the 6th century, the Tabor River moved westward, and sediment from the flooding of the banks began to accumulate rapidly on the river edge in the Forum Aquarium area.
1. River dynamics
Geoarchaeological evidence suggests that a staggering 5.8 meters of sediment had accumulated in the 6th century BC alone. The river sediments are close to the elevation of the Temple of Fortuna, and as a result, in just a few generations, a location that was once largely protected from the threat of flooding has become extremely vulnerable.
Changes in the hydrological regime of the river have also changed the topography of the valley: the banks of the once low-lying river ports have been silted up, and a wide high section of the river bank has emerged in its original place. Sedimentation in the area of Place Boari lasted at least until the 3rd century BC, raising the ground level in parts of the valley by 10 meters.
Based on the available evidence, it is difficult to determine the reason for this change in the position and sedimentary behavior of the Taber. Rivers are highly dynamic and sometimes unstable. They can move riverbeds, erode large areas of land, and form new floodplains. They are susceptible to climate change, fluctuations in precipitation, and even small-scale changes in sediment or hydrological inputs and outputs.
In addition to these forces of nature, however, it must be noted that human activity can create considerable instability in the river landscape. According to the archaeological record, the urbanization of Rome in the 6th century appears to have been rapid and massive. In just a few generations, the Romans reclaimed a considerable portion of the lowlands and invested in the construction of more than a dozen monumental buildings.
To support documented construction activity and presumably a growing urban population, timber will be developed as a building material and a primary fuel source. While much of the area around modern Rome is currently devoid of dense forests, paleobotanical evidence suggests that central Italy was once a dense forest before human settlement.
In addition to the impact on land, deforestation also has a significant impact on river systems. As trees are cut down, sediment can easily erode from the slopes and be washed into the river valley.
Unfortunately, data on ancient pollen is currently limited, making it difficult to track the timeline of local deforestation. However, later anecdotes suggest that by the early 1st century AD, forests as far away as Pisa were being developed to meet Rome's demand for wood. Most likely because the resources close to Rome have been depleted. Although the evidence is uncertain, it highly suggests a link between urban development, deforestation, and change in the Tiber.
The dynamics of the major rivers during this period not only triggered sedimentation capable of complex maneuvers around the river port, but also seemed to have contributed to the increase in the amplitude of flooding. As the city grows, the ground level in the valley rises, and the space to accommodate floods decreases. The available evidence suggests that flooding reached greater heights over time.
Coring surveys in the valley area have exposed the flood sedimentary features of the 6th century BC above 6 m above sea level, and these reached 9 masl by the 3rd century BC.
By the 1st century BC, historical records of Roman floods indicate that buildings were threatened by floods of up to 20 mas at considerable elevations. As paved pavements expanded and buildings eroded, flooding threatened new areas at higher elevations and farther away from the river. The Roman historian Tacitus vividly described this result in his book The Flood That Destroyed Rome in 69 AD.
As the city grew, the flood challenges faced by Rome persisted, and initial mitigation efforts quickly became inadequate to cope with the changing situation.
2. Adapt to changing landscapes and escalating floods
Due to a lack of modern understanding of geological processes, the early inhabitants of Rome could not predict the environmental consequences of their investments in urban infrastructure and deforestation. Nor can they foresee how the pattern of Tiber flooding will change over time, so much so that a generation's adaptation efforts sometimes prove inadequate even in just a few decades.
While the Romans responded in a variety of ways over the centuries, their actions focused on accepting the inevitability of floods and mitigating their effects, rather than trying to prevent floods altogether. The archaeological record shows that the Romans began to adjust their urban investments in the valley in the late 6th century and will continue to do so over time.
Although we lack a single written record of the challenges faced by the Romans themselves until the 3rd century BC, the archaeological evidence is telling. The Temple of Fortuna in the early 6th century, which had only stood for two or three generations on the raised part of the riverbank, was abandoned, and the Romans built a 6-meter-high platform in its place, leaning against the lower side of the Capitoline Hill.
This violent reaction showed that the Romans were adapting to the new threat of flooding. In the early 5th century the renovation of the port sanctuary which required the confiscation of a sacred structure and considerable investment of resources and manpower was built a new, artificial terrace, again standing a few meters above the river. On top of this huge platform, the Romans once again built two new temple buildings on the banks of the river.
This enormous effort to move buildings away from the flood can also be seen elsewhere, notably the Roman Forum, where a series of landfills gradually raised ground levels, presumably in response to increasing flooding.
With the exception of this refuge complex on an artificial platform on the banks of the river and the land reclaimed in the Roman Forum, large swaths of the Roman lowlands were not urbanized for centuries. The process of building in the floodplain alters the ecology, leaving a recognizable mark in the geoarchaeological record: once an area has been laid, the logical expectation is that the sediment deposited by the flood will be cleaned up and not accumulated over time.
In the area of the Forum Boarium, core surveys indicate that sediments continued to accumulate, at least until the 3rd century BC.
We can infer that even though the city of Rome developed significantly in the middle of the Republic, and even though Rome became the dominant power in Italy, the Romans still did not make significant material investments in most of the river valleys.
3. Regional characteristics
Another lowland area, Campus Martius, is similarly used for seasonal events, requiring only minimal urban infrastructure. While the Forum Boarium hosts commercial events, the Martius campus was originally used for military and sporting events. Only sporadic architectural features exist on the Marthes campus, and it was not until the early 1st century that Augustus made a major investment in the area.
By limiting the scale of lowland urban development, the Romans were able to minimize the devastating consequences of flood events. Eventually, urban sprawl, the Roman Empire did extend largely into the valleys, creating new vulnerabilities. There is evidence that as early as the 3rd century BC, the Romans began to invest in the construction of embankments along the river, if not earlier.
These constructions do not appear to have been built to prevent intrusion from the Tiber River. The available evidence of the berm walls of the Roman period suggests that they were low in some areas rather than the kind of cohesive high walls that would have been necessary to contain flooding. On the contrary, these walls have other important uses: to reinforce the riverbank, protect it from erosion, and provide mooring structures to ensure the safety of ships. Above these embankments, new architectural investments will define Rome's riverside landscape.
Most notably, the temple buildings sit on high platforms, which will help them withstand flooding. Even though the valley has been urbanized, the area needs regular maintenance. Among other activities, repeated dredging is needed to remove debris and sediment from the Tiber channel, facilitate vessel navigation activities, and create room to accommodate flooding.
Flood events will require clean-up work to remove sedimented silt and regularly rebuild damaged structures. By the end of the Republic, there was a formal government response.
The bureaucracy, Curretto Res Alve and Tbilis or overseeing the riverbed and banks of the Tiber, presumably to help manage the needs of riverbank maintenance and flood response. With the advent of historical records, we have gained a deeper understanding of the Romans' discussions surrounding the floods that plagued their cities.
Notably, in addition to management and mitigation efforts, they are considering more radical measures to control their turbulent rivers. In the 1st century BC, Julius Caesar proposed the construction of an artificial canal to divert the flow of the Tiber completely away from the city of Rome in order to change the course of the Tiber.
After a devastating flood in 15 AD, Emperor Tiberius appointed a special committee to address the issue. The Roman Senate debated various strategies, including works to divert or dam the Tiber and its tributaries, and to control the volume of water in the river system. However, these radical measures were not implemented in the end.
It must be emphasized that in the late first millennium BC, the ancient Romans already had the engineering capacity to protect cities from floods, whether through the use of dams, artificial levees, canals, or other measures. They carried out many large-scale landscape modifications and hydrological control works within the empire. Therefore, the fact that they did not prevent flooding in the capital is, at least partially, an option, and not completely inevitable.
There are many possible explanations for this seemingly unreasonable judgment, but three reasons should be highlighted. The Romans recognized that rivers were a complex system.
By blocking or redirecting the flow of water, the risk will be transferred to other communities in the area. The damming project was eventually abandoned, in part because of opposition from other communities, who feared increased flooding or loss of farmland.
Technological innovations, particularly the invention of hydraulic concrete in the late 2nd century BC, greatly improved their ability to build urban infrastructure in areas near rivers. The Romans eventually made significant investments in port infrastructure on both sides of the Tiber, securing the import of food and other necessities to support the city with a population of more than 1 million.
The Romans had a religious reverence for the natural world. Many features of the landscape, including the river, are seen as having a sacred essence. Rivers like the Tiber are often anthropomorphized as gods, and natural disasters like floods are interpreted as omins from the gods. Therefore, public efforts to change the environment or control the river will have religious implications.
The reverence of the ancients for the gods should be understood as another adaptive response that provided a certain sense of control over their situation: by appeasing the gods, they might be beneficial to the city and prevent natural disasters.
Affected by the fluctuations of the Tiber River, Rome was devastated by floods and malaria until modern times. In 1870, Rome became the capital of the newly united Italy, and in the generation that followed, a series of major floods inundated large swaths of the city for several days.
Turn-of-the-century photography captures the adaptability of modern Romans, who travel through the city by boat, just as their prehistoric ancestors did. Faced with recurring threats to his new capital, King Vittorio Emanuele II of Italy worked to modernize Rome and organized a commission to develop a plan to prevent such disasters.
Officials discussed various strategies, including revisiting the rerouting of the Tiber River to keep it completely away from the city. Finally, it was decided to carry out a large-scale overhaul of the area along the Tiber.
This area has been heavily encroached upon over the past few centuries. Buildings along the riverbank were demolished, and by the time the project was completed in 1910, the entire river flowing through the city was surrounded by a 40-foot-high concrete wall. After the city was tormented by floods for more than two thousand years. This huge investment in urban regeneration and flood walls ultimately ensured that the lowlands of Rome would be protected from floodplain flooding.
Now, it's not entirely uncommon for cities to experience flooding problems, which are often the unpleasant result of heavy rains and clogged sewer systems in cities. The proximity to the Tiber and the early dependence on the Tiber greatly shaped Rome. In order to build their cities, the ancient Romans had to negotiate a complex relationship with their environment and accept considerable risks.
Archaeological and historical evidence of a wealth of Rome highlights the extent to which river systems can be altered by urban development. In addition, this case study shows that flood risk can be exacerbated over a period of many centuries, and as a result, flood prevention strategies in one generation can prove to be completely inadequate for the next.
The complexity of this urban-river interaction requires a multifaceted approach, leveraging community collaboration and government leadership, to effectively address a variety of challenging issues.
While the answers to these questions will undoubtedly vary from community to community, the global history of resilient riverfront cities can provide valuable perspectives to help policymakers and communities anticipate changing conditions, explore adaptive strategies, manage risk, and look ahead to sustainable growth.
Looking to the past can help us understand where we are in today's world and prepare for the future.