Part of its structure traces back to the construction ordered by King D. Afonso Henriques, in the 12th century. It consists of two symmetrical vaulted arcades.

Large reservoir designed to collect and store rainwater. The mouth of the cistern (an opening in the vault) can be observed on the left side, through which water flows and fills up the area.

The cistern was of great importance as it was the primary source of water for the Monastery’s domestic and agricultural activities and its land.