Winchelsea, place in Rother district, administrative county of East Sussex, historic county of Sussex, England, with historical importance as a former English Channel port and as an example of medieval town planning. Old Winchelsea, reputed to have consisted of 700 houses, 50 inns, and numerous churches, was destroyed by the sea in 1287. New Winchelsea was then built by Edward I (reigned 1272–1307) on higher ground and was laid out in a grid pattern, with the Church of St. Thomas Becket at the centre. Three town gates still stand. From the 12th century Winchelsea was one of the Cinque Ports. Marshes adjoin the spur on which the new town was built. Until the 15th century these were a sea inlet that provided a good harbour, but during the 16th century the inlet became silted up, destroying the port. Only a small village remains.