Founded in 1153, the Abbey became the biggest church in Portugal and one of the most powerful of the Cistercian order. Among its many treasures are the mediaeval tombs of D. Pedro I and Ines de Castro, and sixteenth century pottery by the monks. Internationally acknowledged for the austerity and purity of its architecture, the Abbey became a World Heritage Site in 1985. The Abbey's art and architecture is explored in detail in this guide, with colour photographs, drawings and plans.