York has, since Roman times, been defended by walls of one form or another. To this day, substantial portions of the walls remain, and York has more miles of intact wall than any other city in England. They are known variously as York City Walls, the Bar Walls and the Roman walls (though this last is a misnomer as very little of the extant stonework is of Roman origin, and the course of the wall has been substantially altered since Roman times). The walls are generally 13 feet (4m) high and 6 feet (1.8m) wide. History Roman walls The original walls were built around 71 AD, when the Romans erected a fort (castra) occupying about 50 acres or 21.5 hectares near the banks of the River Ouse. The rectangle of walls was built as part of the fort's defences. The foundations and the line of about half of these Roman walls form part of the existing walls, as follows: a section (the west corner, including the Multangular Tower) in the Museum Gardens the north-west and north-east sections between Bootham Bar and Monk Bar a further stretch between Monk Bar and the Merchant Taylors' Hall, at the end of which the lower courses of the east corner of the Roman wall can be seen on the city-centre side of the existing wall. The line of the rest of the Roman wall went south-west from the east corner, crossing the via principalis of the fortress where King's Square is now located. The south corner was in what is now Feasegate, and from here the wall continued northwest to the west corner. The point where the wall crossed the via praetoria is marked by a plaque in St Helen's Square near the Mansion House. Multangular Tower The Multangular Tower in the Museum Gardens is the most noticeable and intact structure remaining from the Roman walls. It was constructed as part of a series of eight similar defensive towers. The walls are almost certainly the creation of Septimius Severus; however, the Multangular Tower is probably a later addition of Constantine the Great around 310–320 AD. It has ten sides, based on a regular fourteen-sided figure designed so that a circle through the internal angles of the internal face is tangential to the curve. The rear four sides are missing to provide access to the interior of the tower. A low plinth or skirt extends