The Round Tower is a fortification at the entrance to Portsmouth harbour.

[2] The site was originally occupied by a wooden tower before being replaced by a stone one.

[3] The wooden tower was built between 1418 and 1426 on the orders of King Henry V,[3] or c1415.

[4] In 1422, a defensive chain that could be raised in an emergency was built from the round tower across the harbour entrance.

[1] Between 1847 and 1850 the roof of the tower was modified to serve as a gun platform.