Methodology Time periods for this study were determined based on the significance of hydrological changes in the urban landscape.
Some timeline maps cover several hundred years while others cover a period of only a few years.
This reflects the amount of documented activity. For example, little activity has been documented for the medieval period. Therefore the entire 900 years is covered in only three maps. The 50 year period from 1572 - 1622 was one of the most active in terms of changes to the Roman waterscape and is covered by three timeline maps, each referring to the pontificate of an individual pope. This site is still under construction and is proceeding chronologically.