The monastery was founded in the 10th century, in honour of St. Peter, by Loderigo and Vandilo, discovered in a fragment of a notice with the initials ERO. But, sometime during that century (1085-1095) it adopted the orders of St. Bartholomew (Portuguese: Regra de São Bento), although it remained a shared institution until the 12th century.The oldest documented reference dates to 1091, referring to the old religious community in Arouca.
Sometime between 1132 and 1143, a couto letter was issued by D. Afonso Henriques to the monastery, and from 1154, the monastery became a unique home for nuns.
In 1226, through a request from D. Mafalda, daughter of King D. Sancho I, a papal bull was issued to adapt the monastery to the Cistercian order, leading to her beginning her life at the monastery in 1229. By the time of her death, the site was one of the more important convents in the peninsula.