Of all the fortresses in Macau, the Monte castle is the oldest, lying to the east of the Ruins of St. Paul's. Erected in 1616, it initially belonged to St. Paul's Church and was used to guard the cathedral from the pirates. It shortly became exclusively a military fort. The fort is parallelogram with fortresses at each corner and about 100 meters in boundary. Barracks, cisterns and storehouses were the chief buildings of the fortress. An antique tower located here was one of the sites of the Society of Jesus. With mortars on the four sides, the citadel was powerfully equipped. Though the mortars have lost their military function, they still stay on.