Mosteiro de Santa Maria de Alcobaça was founded in 1153 by King Afonso Henriques — the first king of Portugal — as a thanksgiving for the conquest of Santarém from the Moors in 1147. He granted the lands of Alcobaça to Bernard of Clairvaux's Cistercian order, which began construction of an austere new abbey in 1178. The church was consecrated in 1252. For the next six centuries Alcobaça was the most powerful religious house in Portugal, controlling vast agricultural estates across the Estremadura.
Architecturally Alcobaça is the purest expression of Cistercian Gothic in the Iberian Peninsula. The church — 106 metres long, the longest church in Portugal — follows the strict template laid down by the order: tall, narrow, undecorated, with the light controlled by clerestory windows rather than stained glass, and a complete absence of figurative carving in the nave. Cistercian abbeys were designed for contemplation in austerity. The Cloister of Silence — added under King Dinis in 1308 — is one of the great rooms of medieval Portugal.
The abbey's most-visited feature is the pair of royal tombs in the transept: King Pedro I, who died in 1367, and Inês de Castro, his Galician lover whose murder by court order in 1355 set off the dynastic crisis of the late 14th century. After his accession Pedro had Inês exhumed, crowned posthumously, and placed in this matched pair of carved limestone tombs, foot-to-foot, so that on the Day of Judgement, when the dead rise, they would see each other first. UNESCO inscribed the monastery as a World Heritage Site in 1989.