The great tower, or keep, still dominates the headland upon which Scarborough Castle stands. It was built by Henry II between 1159 and 1169. From its lofty position the tower overlooks the town and all approaches to the castle from both land and sea. The building was ruined by an intense bombardment during the siege of 1644/5 (English Civil War). This caused the collapse of the western wall and left tower much as it is seen today.

The great tower is a vast structure; more than 27m (90ft) high and is set out on a square plan with walls 3.5m (12ft) thick.