North-west Angle Tower. This is the position of the stone tower at the north-west corner of the Roman fortress. It was built soon after A.D.103, and was discovered during the construction of St. Martin's Gate in 1965. The tower was 30 feet wide and 27 feet deep, with walls a little over 4 feet thick. It marks the point at which the Roman and Medieval defences diverge. The fortress was here turning southwards towards Holy Trinity Church which is on the site of the Roman west gate (porta principalis dextra).