That wheel was powered by water flowing through a canal that passed under the castle building, which was then released out ...

Researchers have excavated the ruins of a medieval castle buried beneath ... mill room’s grated exit, where water would have flowed out to an exterior moat that bordered the fortress.

Each castle had gates, often with a metal barrier called a portcullis and with doors made of a very strong wood. And sometimes they had a moat, which is a ditch filled with water to stop people ...