Started in 122ad Hadrian's Wall was built across the North of England on the orders of the Emperor Hadrian. It is 117 kilometers long and is built in stone. In places it is six meters high and three meters wide - enough for two soldiers to do sentry duty side-by-side. Every Roman mile (about 1500 meters) a mile-castle was built which housed twenty soldiers. Turrets guarded by soldiers were built every 500 meters. Major forts were built along the wall at every eight kilometers. These could accommodate between 500 and 1000 Roman soldiers. All the building was done by the Roman soldiers themselves. They were trained to do this and the army had its own skilled engineers who designed the wall. That so much of the Wall has survived is a testament to their building skills.