The Castle of Belver (Portuguese: Castelo de Belver) is a Portuguese castle in the civil parish of Belver, municipality of Gavião, district of Portalegre, in central Portugal. Belver was the first castle and most important to be constructed by the Hospitallers in Portugal during the Middle Ages. It was built in order to defend the access-way along the Tagus River, and donate by Sancho I under the condition that a castle be constructed. In 1194, King Sancho conceded this region of the Northern Tagus River, then known as Guidintesta, or Guidi in testa (or still of Costa), to Afonso Paes, prior of the Order of the Hospitallers. By so doing, the King hoped to stabilize the Christian-Muslim frontier along the Tagus River, leaving the Templar to almost monopolize their power along the frontier lands. The King began referring to the construction of the Castle and the surrounding as Belver. In his later testament, King Sancho transferred the title of the Castle to the Hospitalers. By 1210, construction was far enough advanced to allow the permanent occupation and defence. The testament while identifying its existence, also made it clear that the Castle was one of the six repositories of the nation's wealth, thereby providing ample proof of the Castle's defences, albeit located in a frontier outpost. The final construction was completed in 1212.