The stone tower was built around 1250, probably at the end of a wall or earthwork leading to Castlegate, around the moat of York Castle.
It was first recorded in 1315, and by 1424 the part of the city inside the walls was occupied by the York Franciscan Friary.
[1][2] Around 1730, the tower was altered, when a summerhouse was constructed in its southern corner: the basement in stone, and the raised ground floor in brick.
[1][2] The mediaeval stone wall is about 10 feet high and 1 foot 8 thick, and it retains two original windows: an arrowslit in a cross shape, and a musket loop.
Some internal features survive from the 18th century, including a chimneypiece, window seats, a dado rail with panelling, and a cornice.