There are 22 watch towers distributed at close intervals along the wall. They are located not only in the main wall but also at the distinctive 'branch cities'. Branch cities are built on the hill ridge against the inner or outer side of the wall. They measure from several yards to dozens of yards across. On the northwest over 3,281-feet hills, lies a section of the wall called 'Ox Horn Edge'. On the steep and lofty peaks, there are two walls named 'Flying Eagle Flies Facing Upward' and 'Arrow Lock'. What is more rarely seen on the southeast side is a general gateway platform guarded by three watch towers together. In locations of strategic importance, batteries are set up to reinforce the defense capabilities. Mutianyu really deserves to be the archetype of the ten thousand li Great Wall.