The site of Carisbrooke Castle, near Newport, Isle of Wight may have been occupied in pre-Roman times.. The existence of a ruined wall suggests there was a building there in late Roman times. The Jutes may have taken over the fort and the by the late 7th century. An Anglo-Saxon stronghold occupied the site during the 8th century. Around 1000, a wall was built around the hill as a defence against Viking raids. After the Norman Conquest, William the Conqueror gave the Isle of Wight to his friend William FitzOsbern who built a wooden structure. The castle is mentioned in Domesday book under Alvington, and was probably raised by FitzOsbern, who was made first lord of the Isle of Wight.
From this date lordship of the Isle of Wight was always associated with ownership of the castle, which thus became the seat of government of the island. Henry I gave it to Richard de Redvers, in whose family it continued until Isabella de Fortibus sold it to Edward I, after which the government was entrusted to wardens as representatives of the crown. The castle was garrisoned by Baldwin de Redvers for the Empress Maud in 1136, but was captured by Stephen. In the reign of Richard II it was unsuccessfully attacked by the French (1377). The keep was added to the castle in the reign of Henry I, and in the reign of Elizabeth I, when the Spanish Armada was expected, it was surrounded by an elaborate pentagonal fortification by Sir George Carey.
Charles I was imprisoned here for fourteen months before his execution. Afterwards his two youngest children were confined in the castle, and the Princess Elizabeth died there. In 1904 the chapel of St Nicholas in the castle was reopened and re-consecrated, having been rebuilt as a national memorial of Charles I. Within. the walls is a well 200 ft. deep; and another in the centre of the keep is reputed to have been still deeper.
Much of the text from Encyclopedia Britannica 1911