Hadleigh Castle is a ruined fortification in the English county of Essex, overlooking the Thames Estuary from south of the town of Hadleigh. Built after 1215 during the reign of Henry III by Hubert de Burgh, the castle was surrounded by parkland and had an important economic and defensive role. The castle was significantly expanded and remodelled by Edward III, who turned it into a grander property, designed to defend against a potential French attack, as well as to provide the King with a convenient private residence close to London. Built on a soft hill of London clay, the castle has often been subject to subsidence; this, combined with the sale of its stonework in the 16th century, has led to it now being ruined. The remains are now preserved by English Heritage and protected under UK law as a Grade I listed building and scheduled monument.