The length and size of the wall made it one of the biggest construction projects in Roman Britain. It had gateways, towers and defensive ditches, and was built from Kentish ragstone, which was brought by barge from quarries near Maidstone. It was long, enclosing an area of about . It was to wide and up to high. The ditch or "fossa" in front of the outer wall was deep and up to wide. There were at least 22 towers spaced about apart on the eastern section of the wall.