The old triangular Viking city was enlarged after the Anglo-Norman invasion of 1170 when many fortifications were rebuilt or strengthened. The fortifications that ran along the south-eastern side of the city connecting Reginald's Tower to St. Martin's Gate were rebuilt in stone prior to 1208 together with the wall that ran north from St. Martin's Gate to Turgesius's Tower on the quay.

Reginald's Tower, St. Martin's Gate and Turgesius's Tower were the three terminal points of a triangular shaped enclosure which in about 1210 corresponded roughly to the area covered by the old Viking city.

Excavations carried out in 1983 uncovered the remains of St. Martin's Gate, a 13th century gate and portcullis flanked by twin towers.

The passage or entrance was kept narrow to hinder invaders and to facilitate the collection of the murage tax levied on goods brought into the city.