Nearly every sizable European city dating to the Middle Ages or earlier had defensive moats on accounts of wars waged between various duchies, kingdoms, and empires. Some of these moats were manmade and others were modified natural streams. Along with moats, every city had a millstream whose water was harnessed to produce grain for the residents. When moats and milldams became obsolete, they were reduced in size, filled, or retained as water features in parks.
Above is the Kaitzbach stream flowing through the Große Garten park in Dresden, Germany. Here, it widens into the Carolasee lake before disappearing under the city’s streets. The postcard dates from 1914, the year when imperial Germany plunged into the First World War.
Hidden Waters blog 