The headland at Scarborough is an ideal site for a castle. The highest point on the headland is some 100ft higher than the lowest point on the spit of land connecting it to the mainland, and it is surrounded by steep cliffs on three sides. The site was in use long before the castle was built, and the headland contains an iron-age settlement and a Roman signal station as well as the impressive ruins of the medieval castle.
A wooden fort was built soon after the Normans arrived in the area, but the first stone castle wasn’t built until 1135-36. This was a private castle, owned by William de Gros, earl of Albemarle or Aumale, but Henry II soon decided to take it over as a royal castle. It was Henry who built the keep, between 1158 and 1175. According to the evidence of the Pipe Rolls this cost £683, the seventh largest amount of money spent on any castle by Henry. The keep is 55ft square and was probably 100ft high, with four un-vaulted stories. The main (first) floor had a flying arch, and was approached via a forework containing stairs on the southern side of the building. The keep was of rough stone and mortar construction, faced in dark red sandstone dressed masonry and with a leaded roof. The forework containing the entrance stairs was 40ft height, 20ft wide and 30ft long, making it a large building in its own right.
Most of the wall that cuts across the headland is Norman, although the half round towers probably date to the 13th century. The walls are 20ft high and protected by a ditch. A barbican was added in the thirteenth century, straddling the ditch and protecting the entrance. The area around the keep was surrounded with its own walls and ditch, producing an 'inner ward' which contained the 170ft deep well. The outer part of the castle, protected largely by the cliffs, contained the domestic buildings, including a hall, kitchen and chapel. The sea cliffs were normally seen as a sufficient defence of the outer part of the castle, although a 1538 report noted three places where they could be scaled and mentioned the lack of any towers, walls or turrets.
Scarborough castle was besieged on several occasions. In 1312 Piers Gaveston, a favourite of Edward II, attempted to make a stand in the castle while being pursued by hostile barons. He was forced to surrender and was then murdered despite having been assured of his safety.
In 1645 a Royalist garrison under Hugh Chomley was besieged by the Scots under John Meldrum. The keep was badly damaged by Scottish artillery before the garrison surrendered with its honour intact, marching out of the castle.
In 1648 the Parliamentary garrison mutinied and went over the Royal side after not being paid. Once again the garrison was starved out.
After the Jacobite revolt of 1745 barracks were built inside the castle.
In the late 19th century a coastguard station was built on top of the Roman signal station (unknown to the builders when they started).
On 16 December 1914 a squadron of German warships bombarded the town, firing 500 shells. The coastguard station and barracks were wrecked and the keep was damaged.