What makes this particular survival so quietly odd is how thoroughly the walls have been domesticated. The west walls of houses numbered 1 to 4 Verdant Place, for instance, display a slight but unmistakable external batter, the angled base that medieval builders used to give town walls stability and resistance to undermining. The medieval fabric did not disappear so much as become load-bearing real estate.

The defences of what was known as the English Town have their origins in the Viking period, though the precise line of those earliest walls remains uncertain. Murage grants, which were Crown licences allowing a town to collect tolls specifically to fund wall-building, are documented from as early as 1237, with further grants recorded in 1310 to 1311, 1375, and 1400. Work continued into the fifteenth century; a locally kept account known as the Arthur Manuscripts records that Cogan's Tower on the east side of Irishtown was completed around 1430. The course of the later medieval defences can be traced with reasonable confidence from a series of maps: the Hardiman map of around 1590, the Pacata Hibernia map of around 1600, John Speed's map of 1610, Thomas Phillips's view and map of around 1685, and the French map of 1691. One genuine puzzle that these maps raise concerns a cross-wall shown on Phillips's map running from the Shannon eastward along Newgate Lane, bisecting the English Town entirely. Whether this represents a remnant of the Viking circuit or served some later purpose remains unresolved, since either interpretation requires placing important early landmarks inconveniently outside the walls.

Several stretches of wall and two mural towers survive on the north and north-west sides of the island and are accessible without any special arrangement. The section running along the graveyard north of Castle Street retains its roughly coursed limestone blocks and stands to around 5.1 metres externally, though the interior ground level has risen so much over the centuries that the wall barely clears head height from the inside. A second tower, approximately 45 metres further north and forming the north-west angle of the defences, preserves a blocked arrow loop facing north-west and what may be the original wall-walk ledge on its inner face. A further substantial stretch, around 7 metres high externally, survives in the gardens of St Mary's Convent near the north-east angle, where the large dressed limestone blocks and a pronounced base batter are clearly legible. Ivy is a persistent problem at the tower sites and can obscure features that are present but not immediately visible.