It is dry now but once it used to fill with water as the river Thames rose and fell with the tide, the 2000 people that lived in the tower had their well... "waste" piped into it. It did a great job of keeping out the enemiesbut was also home to a lot of disease and become very unpleasant at low tide.
Moat of Tower of London.JPG - 2048 x 1536 - (1.33MB)