The cistern (from the Arabic al-jubb) is one of the very few remains of the old Great Mosque after it was destroyed. It is a vaulted brick construction for storing water, especially rainwater, which was used by the faithful to wash themselves before prayer by means of wudu or ablution. It is located under the floor of the main altar of the present-day Church of Santa Maria and is accessed through the courtyard. Al-Wansharisi (15th c.) mentions the mosque in his work when he refers to how the peasants arrived in Vélez and... "They would go to the square in front of the main mosque where they exchanged goods for oil, and brought the figs to the courtyard of the mosque, spread them out in the sun and packed them".