A plaque fixed to one section reads 'The Old Wall of Athlone 1251', which is not quite the whole story. The surviving fabric here, including the best-preserved bastion in the town, was actually built during the Cromwellian period, between 1651 and 1654. The medieval origins are real enough, but what the eye sees today is largely a product of seventeenth-century military engineering, layered over and often replacing what came before.

The story of Athlone's defences is one of repeated construction, neglect, and reconstruction driven by strategic necessity rather than civic pride. A royal payment of eighty marks was ordered in 1251 to help enclose the town and repair its castle, though it is unclear which side of the Shannon that money reached. By the late sixteenth century the walls had fallen badly into disrepair. Sir Nicholas Malby drew up proposals to rebuild them in 1576, but they appear to have gone no further than the draft stage. Real work came under Lord Wilmot, President of Connacht, as part of the Crown's plantation of Westmeath. In a submission to Charles I, possibly written around 1627, Wilmot noted that he had been charged with building and walling the town, that most of the work had been done seventeen years earlier, and that the condition attached to land grants from James I, namely that inhabitants build with brick and stone and wall the town well, had been fulfilled. A state paper from 1630 spells out the strategic logic plainly: the walling of Athlone was seen as essential to guarding the bridge and consolidating English power across the inland regions. The Cromwellians then added several bastions to the Leinster side between 1651 and 1654, and it is this phase of work that produced most of what survives. Writing in 1682, Sir Henry Piers described the Leinster defences in their prime: strong walls with large flankers of lime and stone, a rampart of stone and earth lining the inside, a deep fosse outside, and cannon mounted on the bastions. He also noted that even by his time the Connacht side had already largely vanished. The Jacobite improvements of 1689 to 1691 were the last before the Dutch general Ginkel assaulted and largely demolished the fortifications in 1691.

The most substantial fragment still standing is the so-called Garden or Royal Bastion, a Cromwellian-era structure with all four sides preserved and an exterior batter, the slight outward lean at the base designed to deflect cannon fire and make undermining harder. The wall running from Lucas Lane to the rear of the hotel is roughly 1.9 metres long in the surviving section, 1.5 to 1.6 metres wide, and 1.85 metres high, and retains both a semi-circular tower and part of a further bastion alongside the complete one. The North Gate, which once stood at the junction of Lucas Lane and North Gate Street and was recorded by George Petrie in a print of around 1820 as a three-storey battlemented structure, is entirely gone. Last remnants south of the gate were removed when the Radisson hotel was built.