Hadrian's Wall, a UNESCO World Heritage site in northern England, was a massive Roman fortification built starting in 122 AD under Emperor Hadrian to mark the Empire's northwest frontier, separating Roman Britannia from "barbarian" lands to the north, featuring a stone wall, forts, milecastles, turrets, and defensive ditches like the Vallum. Stretching 73 miles coast-to-coast, it wasn't just a barrier but a controlled border for trade and troop movement, evolving into a bustling frontier zone with settlements around its forts, and remains a significant historical landmark today.
