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United Kingdom

A low remnant of Hadrian’s Wall. The defensive fortification was built by the Romans over six years beginning in A.D. 122 and then strengthened in subsequent decades. Named after the emperor who ordered its construction, the barrier secured the northwest section of the empire from barbarians. The 117.5-km (73-mi) wall stretches across England from Wallsend in the east to Solway Firth in the west and was designated a UNESCO World Heritage site in 1987.