Newark Castle, in Newark, Nottinghamshire, England, is said to have been founded by Egbert, king of the West Saxons, was partly rebuilt and greatly extended by Alexander, consecrated Bishop of Lincoln in 1123, who established it as a mint. His rebuild here was probably the model for that at Sleaford Castle, also built by Alexander. It rises picturesquely from the river, and from its position and great strength was for a long time known as the 'Key of the North'. Of the original Norman stronghold the most important remains are the gate-house, a crypt and the lofty rectangular tower at the south-west angle. The building seems to have been reconstructed in the early part of the 13th century. King John of England died at this castle on 19 October 1216. In the reign of Edward III it was used as a state prison. During the English Civil War it was garrisoned for Charles I, and endured three sieges. Its dismantling was begun in 1646, immediately after the surrender of the king.