Although Pembroke Castle is a Norman-style enclosure castle with great keep, it can be more accurately described as a linear fortification because, like the later 13th-century castles at Caernarfon and Conwy, it was built on a rocky promontory surrounded by water. This meant that attacking forces could only assault on a narrow front. Architecturally, Pembroke's thickest walls and towers are all concentrated on its landward side facing the town, with Pembroke River providing a natural defense around the rest of its perimeter.