Hadrian’s Wall, ancient Roman stone and masonry wall, constructed to protect the northern boundary of Roman Britain against hostile tribes. Emperor Hadrian of Rome ordered its construction around ad 122. The wall extended 117 km (73 mi) from Solway Firth to the mouth of the Tyne River and was about 6 m (about 20 ft) high and about 2.4 m (about 8 ft) wide. A military road ran along the south side of the wall, and a series of heavily garrisoned forts and sentry posts were built along its length. The wall also marked the frontier of Roman civil jurisdiction. A few sections of Hadrian's Wall remain standing in present-day Great Britain.