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