Castle well

A castle well was a water well built to supply drinking water to a castle. It was often the most costly and time-consuming element in the building of a castle, and its construction time could span decades.

The well – as well as any available cisterns – provided a protected source of drinking water for the castle garrison in peace and war and also for any civil population seeking refuge during a siege. In medieval times, external wells were often poisoned, usually with a decomposing body, in order to force a garrison to surrender. But wells sunk within the castle itself could not be poisoned from outside during a siege.