Enclosure castle constructed in C13 by Robert of Tattershall. Licence in 1231. In C15 it passed to Ralph, first Lord Cromwell, who rebuilt it as a fortified house and founded a college on the adjacent site. The castle was ocupied until 1693; it thereafter fell into disrepair in the years after 1912 restoration was undertaken by Lord Curzon under the direction of William Weir, architect. The remains take the form of an inner moated enclosure with two enclosures, also moated. Parts of the curtain wall survive in the western part of the enclosure adjacent to the later Great Tower. The foundations of two interval towers also survive, to the north and south of the Great Tower. The remains of another interval tower have been identified on the south side of the enclosure. Construction of the Great Tower commenced in the 1430s when the castle was converted into a fortified residence. The Great Tower is an outstanding red brick tower in English bond, with darker lattice lozenge decorations to upper parts, ashlar dressings, leaded roofs. Rectangular plan with facetted angle towers, originally with attached hall to courtyard side. 5 storey with undercroft, irregular 3 bay front with plinth, chamfered ashlar string course and embattled parapet with machicolated base.