In 1957 Frank Jenkins excavated a Medieval tower against the city wall in the site of the Old Cattle Market, 61m south of St George's Street. The tower appeared had Roman a predecessor, although the inner area of the city wall was not investigated meaning an internal tower may yet be found.
The Roman wall stood to a height of 0.9m including footings, but it could be seen to change direction at this point. The NE side of the Roman tower survived as a stump of flint and mortar projecting out from the city wall. It clearly abutted the wall, and could be seen to be of later construction, added, presumably, in the 4th century. Elsewhere the tower had been badly robbed, leaving only the rubble-filled foundation-trench. This had been sunk to the same depth as the Roman wall-trench and extended out from the face of the wall for c. 1.5m. Beyond this it had been largely destroyed by the deep foundations of its Medieval successor. However, the outer edge of the Roman tower's foundation-trench was seen just under the NE side of the Medieval tower; the angle at which it lay in relation to the city wall suggested that the tower was horse shoe shaped and presumably hollow.
There was evidence for iron-working in this area before the construction of the Roman defences. Above the natural gravel was a band of greenish-brown loam containing decayed bones, and sealing this a low mound of white ash, charcoal, burnt clay and several lumps of iron slag. These extended under the foundations of the city wall. Cut into the mound was a shallow pit 30cm in diameter and just penetrating the surface of the natural gravel. It yielded several pieces of iron slag and may have been a primitive iron-smelting furnace.

Frere, SS, Stow, S, and Bennett, P, 1982, Excavations on the Roman and Medieval Defences of Canterbury. (Monograph). SKE28530.