From the time that a permanent settlement was established in the late second and early first millennium bce, Rome has been influenced in its development by its physical environment.1 Certain natural topographical features were obvious contributors to the city’s pattern of growth, such as the proximity of the Tiber’s flow that was both fordable and navigable and that connected both sea and road traffic to the city’s walls.2 The individual hilltop villages were defensible, and gradually they coalesced into a unified community.3 The marshy ground nestled between the rises of the Capitoline, Palatine, and Viminal Hills proved perfect for creating a political, religious, and commercial center, ultimately the Roman Forum, where the first Senate house was built in the early sixth century bce.4 Volcanic lakes and streams in the Alban Hills, shaped by pyroclastic flows millennia earlier, provided a source for drinking water that could be carried at an acceptable gradient for many miles to the cisterns and fountains that have served the city to the present.5 Even the wide floodplain north of the Capitoline that was challenged for centuries by annual inundations from the Tiber and malaria-carrying mosquitoes proved eventually suitable for enormous imperial entertainment venues and the shops and apartments found there today.