Floods of the Tiber in Ancient Rome

Aldrete’s book on the floods of the Tiber is timely, coming out so soon after Hurricane Katrina and the catastrophic flooding of New Orleans. As the author notes (258 n. 5), his manuscript had already gone to press when Katrina landed in August 2005, so he was not able to incorporate the studies that emerged soon after, which is probably fortuitous since the vast amount of new literature could easily have delayed the publication of this excellent study.

The goal of the book is threefold: to gather what is known in order to establish the characteristics of the Tiber floods, to examine the effects of the floods on the inhabitants of Rome, and to explore how the Romans responded to the floods. The discussions are all presented in a clear and readable manner so that the reader always knows where the author is going, why he is going there, and what methodology he will use to get there.

Aldrete begins by collecting the primary evidence: 42 literary accounts for 33 floods dating from 414 B.C.E. to 398 C.E. Each relevant passage is presented in the original language followed by an English translation. By combining information gleaned from these sources with a topographical map of Augustan Rome, he is then able to present the magnitude of various ancient floods. So, for example, Dio’s description of the flood of 12 C.E. states that the Circus Maximus (15 masl) was flooded, whereas the Forum of Augustus (17 masl) was not. Aldrete thus determines that the waters reached a level of 15–16 masl, which falls into his category of extraordinary flood. All recorded floods, both ancient and modern, are collected in appendix 1, which reveals that the highest documented flood was 19.56 masl, in 1598. By analyzing a passage from Cicero describing the flood of 54 B.C.E. in a similar manner, Aldrete determines that it rivaled the 1598 flood at about 20 masl. Having established such limits, he can then determine which major public buildings were typically not affected by floods, such as the public baths (with the early exceptions of the Baths of Agrippa and Nero). One can also use information provided by Aldrete to calculate the effects of major changes in the topography of Rome that postdate his Augustan map, such as when Nero’s lake was created after the fire of 64 C.E. by raising the ground from 15.5 masl to ca. 22 masl, thus putting it beyond the reach of even the most major flood.

In addition to establishing the magnitude of floods, Aldrete also discusses their duration (one to three days, with a maximum of five days), seasonality (winter/spring), and frequency (major flood every 20 years). In explaining how these figures are established, he also gives a clear and comprehensible explanation of hydrology in general and in particular that of the Tiber and its basin. He consistently returns to his primary ancient sources to make the modern scientific information relevant to the ancient floods.

The second goal of determining the effect of floods on the inhabitants makes up the middle third of the book. This section is somewhat more speculative, providing less direct insight into ancient Rome since the literary evidence is less forthcoming, but it is nevertheless a fascinating read. He recreates a “virtual” flood to give a sense of what people would have had to face in a flood crisis. He deals with destruction of property, collapse of buildings, injuries, cleanup, food spoilage, disease, and psychological effects. He provides ancient evidence, both literary and archaeological, wherever possible. The descriptions of problems of sanitation and disease are well documented (and graphically described) and indeed coincide with many familiar, post-Katrina newscasts. With regard to ancient Rome, the discussion of factors affecting grain spoilage is particularly enlightening, providing data on moisture and temperature requirements for mold formation (>14% humidity at >5˚C) and modern comparanda for spoilage rates.

The last section of the book deals with the Roman response to floods including an examination of flood-control methods (dams, drains, dikes, canals), as well as social and religious factors affecting attitudes toward floods. Ultimately he brings up one of the main questions of the study: Why did the Romans not do more to protect the capital city from floods? Aldrete’s answer focuses on five factors: (1) the hilly nature of Rome provided nearby refuge on high land in most parts of the city; (2) the use of stone, brick, and concrete created major public structures that could withstand the effects of floods (and the loss of those structures that did not survive was perhaps a good riddance); (3) the people most affected by floods were the less fortunate living in the floodplains, whereas the wealthy, who made public policy, lived in the higher, unaffected parts of the city; (4) the design of grain horrea with high windows, thick exterior walls, and raised floors mitigated some of the damage to the food supply; and (5) the aqueduct system provided clean water originating from above the city so that it was not contaminated by the flood waters, therefore, clean drinking water was always accessible. The question of why Rome resisted flood control came to my mind during a recent visit to an impressive (and presumably effective) Roman dam upstream from Aizanoi in Phrygia. One of Aldrete’s discussions that sheds light on this conundrum deals with the accounts of the strong resistance by Rome’s upstream neighbors to proposals for installing dams to limit the discharge onto Rome after the floods of 54 B.C.E. and 15 C.E. Unlike Aizanoi, which is located in a sparsely populated area, Rome could not simply dump her excess water onto landholders upstream. The situation thus illustrates the complex relationship between politics and technology in the ancient world.

This book is clearly written, carefully crafted, methodologically rigorous, and full of fascinating and insightful discussions. It is well worth a read whether one thought one was interested in floods or not.

Lynne C. Lancaster
Department of Classics and World Religions
Ohio University
Athens, Ohio 45701
lancaste@ohio.edu