Batalha Monastery (Mosteiro de Santa Maria da Vitoria de Batalha) is a magnificent example of medieval Portuguese architecture. In 1385, King Joao I vowed that if his outnumbered army defeated the Castilians at the important Battle of Aljubarrota, he would build a magnificent monastery dedicated to the Virgin Mary. At the north-west corner a multifoliated screen encloses a square for a fountain. The whole cloister is so rich in carvings that it resembles the finest piece of lacework in stone. The octagonal structure is illuminated with tall stained glass windows and topped with an exquisite star vault. The Monastery was designated a World Heritage Site in 1983.