out from the lowest course. The tower stands almost tall, has an external diameter of at the base and above the skirt. Length of each side varies from to on the inner face. The tower projects beyond the curtain wall to a distance of . The foundations are concrete, atop which the tower extends having a rubble and mortar core between ashlar faced courses of small magnesian limestone blocks. At a scarcement reduces the thickness of the wall from to , which continues for a further before being capped by of 13th century masonry in which arrowslits can be seen. After the Romans The Danes occupied the city in 867. By this time the Roman defences were in poor repair, and the Danes demolished all the towers save the Multangular Tower and restored the walls. The majority of the remaining walls, which encircle the whole of the medieval city, date from the 13th – 14th century. From the east corner of the Roman walls, the medieval wall extends to Layerthorpe Bridge. After the bridge, the King's Fishpool, a swamp created by the Normans' damming of the River Foss, provided adequate security for the city, and no walls were ever built in this area. In the Middle Ages the defence of the city was further helped not just by the walls but on the rampart underneath and the ditch surrounding them. The ditch along the walls was once 60 feet (18.3m) wide and 10 feet (3m) deep. In modern times the ditch was almost all filled in and no longer exists. For this reason the ground directly around the walls is higher in most places than it would have been in medieval times. The walls resume beyond the now canalised Foss at the Red Tower, a brick building which has been much restored over the years. They continue south and west around the Walmgate area, terminating in another tower (Fishergate Postern), near York Castle, which was formerly surrounded by its own walls and a moat. A small stretch of wall on the west side of Tower Gardens terminates at Davy Tower, another brick tower located next to the River Ouse. This originally ran up to the castle walls, with a postern on Tower Street. Beyond the Ouse, the walls resume at Skeldergate, where there was once another postern. They climb past Baile Hill, take a right turn and proceed north-west parallel