Carmarthen Castle is a ruined castle in Carmarthen, West Wales, UK. First built by Walter, Sheriff of Gloucester in the early 1100s, the castle was captured and destroyed on several occasions before being rebuilt in stone during the 1190s. The castle was captured by Owain Glyndŵr in 1405. Henry VII's father died at Carmarthen Castle in 1456. During the Wars of the Roses the castle fell to William Herbert and, during the Civil War, was captured by Parliamentary forces. It was dismantled by order of Oliver Cromwell in the mid 1600s.

In the United Kingdom, the term listed building refers to a building or other structure officially designated as being of special architectural, historical, or cultural significance; Grade I structures are those considered to be "buildings of exceptional interest". Listing was begun by a provision in the Town and Country Planning Act 1947. Once listed, strict limitations are imposed on the modifications allowed to a building's structure or fittings. In Wales, the authority for listing under the Planning Act 1990 rests with Cadw.