 It was expanded repeatedly to strengthen the fortifications, the galleries passing underneath the town mounting and descending the various hills.It has a rainwater storage harvesting system, with the largest tank having a capacity of 300,000 liters.The Santa Cruz Chapel was built by the Bishop of Oran at the place where he had carried the statue of the Virgin Mary in a procession, followed by the people of the city, to the Oran hill, when a cholera epidemic had affected the people of Oran, in 1847.