By about AD 105, the Romans pulled out of Pictish Caledonia (Scotland). The border of Britannia was set between Coria (Corbridge) and Luguvalium (Carlisle). In AD 122, the Emperor Hadrian visited Britain and decided to build a big wall of stone with deep ditches along the border at this point. It was called Hadrian's Wall. The western part was wooden at first. It was 117km long, 4.5m tall and between 1.75 & 3m thick. It went both up over craggy mountains and down through flat valleys. It would keep the Picts out of Britannia. In the AD 140s, the Emperor Antoninus Pius sent his armies back into Caledonia. They built a 2nd wooden wall with big earth banks between the River Clyde and Forth. It was called the Antonine Wall; but they only stayed 20 years. Then Hadrian's Wall became the border again. Hadrian's Wall was built by the legions. It was garrisoned by auxiliary units. The numbers of soldiers on the Wall fluctuated (went up and down) over the years. The soldiers lived in forts, milecastles and turrets built along the Wall: There were 16 forts along the Wall, and 5 supply forts just to the south. Each one could house a whole cohort. Every Roman mile (about 1.5km), there was a milecastle. These could house up to 64 soldiers, but usually had less. There were 2 turrets between each pair of milecastles. These were garrisoned by 4 soldiers. They were like 2-storeyed castle towers. Downstairs was for cooking and storage. Upstairs was for sleeping. The roof was the lookout station. Beacons could be lit to warn of attacks from the Picts. The signal could then be sent along the Wall from turret to turret. In the late 4th century, a Roman commander in Britain called Magnus Maximus thought he should be Emperor. So he took a lot of the soldiers from the Wall to Europe to help him. After that, local soldiers tried to protect it, led by tribal warlords. The Wall fell into disrepair though and there were many attacks by the Picts.