The Traitors' Gate is an entrance through which many prisoners of the Tudors arrived at the Tower of London. The gate was built by Edward I to provide a water gate entrance to the Tower, part of St. Thomas' Tower, a section of the tower designed to provide additional accommodation for the royal family.
In the pool behind Traitors' Gate was an engine that was used for raising water to a cistern on the roof of the White Tower. The engine worked originally by the force of the tide or by horsepower and eventually by steam. In 1724–1726, it was adapted to drive machinery for boring gun barrels. It was removed in early 1866.