The town was already described in the 11th century by the Arab geographer Al-Bacr and later by the poets Luís de Camões and Lord Byron (Childe Harold's Pilgrimage - 1809). The Moors built the Castelo dos Mouros in the 8th or 9th century. When Afonso Henriques, with the aid of Crusaders, recaptured Sintra in 1147, much of the castle was destroyed. Only four square towers, the battlements, and the ruins of a Romanesque chapel survived.

In 1493, Christopher Columbus sailing for the Spanish crown, was blown off course by gale force winds and fearing for the survival of his ship, spotted the Rock of Sintra. Despite the awkwardness of seeking safe harbor in Portugal, Columbus had no choice under the circumstances and sailed from there into the Port of Lisbon.