The four surrounding walls of Baghdad were named Kufa, Basra, Khurasan, and Syria; named because their gates pointed in the directions of these destinations. The distance between these gates was a little less than . Each gate had double doors that were made of iron; the doors were so heavy it took several men to open and close them. The wall itself was about 44 m thick at the base and about 12 m thick at the top. Also, the wall was 30 m high, which included merlons, a solid part of an embattled parapet usually pierced by embrasures. This wall was surrounded by another wall with a thickness of 50 m. The second wall had towers and rounded merlons, which surrounded the towers. This outer wall was protected by a solid glacis, which is made out of bricks and quicklime. Beyond the outer wall was a water-filled moat.