Hadrian's Wall, ancient Roman wall, 73.5 mi (118.3 km) long, across the narrow part of the island of Great Britain from Wallsend on the Tyne River to Bowness at the head of Solway Firth. It was mainly built from c.A.D. 122 to 126 under Emperor Hadrian and was extended by Emperor Severus a century later. The wall demarcated the northern boundary and defense line of Roman Britain. Fragments of the wall, 6 ft (1.8 m) high and 8 ft (2.4 m) thick, and many of the "mile stations" (stone blockhouses along the wall constructed every Roman mile) remain. Hadrian's Wall, which has been preserved, is one of the largest and most significant remains of the Roman occupation.