It was once the largest of four bastioned forts, a type of earthwork fortification with angled projecting points designed to eliminate blind spots in defensive fire, thrown up around the southern quarter of Limerick city during one of the most consequential sieges in Irish history. It outlasted that siege, was reoccupied and fought over twice more within forty years, renamed at least once, and then quietly levelled sometime before the middle of the eighteenth century. By around 1752, when William Eyres produced his map of Limerick, it had already been erased from the landscape entirely.

In May 1651, Lieutenant-General Henry Ireton advanced on Limerick with a Parliamentary army of 8,000 men. After attempts to enter from the Clare side of the Shannon were repulsed, Ireton moved his forces south of the city and by late June his engineers had begun constructing a network of ditches, earthen ramparts, and forts intended to encircle the southern section known as Irish Town. The arc of siegeworks ran from Singland Hill in the north to the river's edge in the west, incorporating four bastioned forts at strategic points. The largest, known as Ireton's Fort, sat on an eastern spur of Singland Hill and was garrisoned alongside the adjacent Cromwell's Fort by 800 soldiers apiece. By September, plague and starvation were doing much of the Parliamentary army's work for it. In late October, Ireton identified a section of the town wall not reinforced by earthen ramparts, trained a battery of 28 siege guns on it, and began pounding. Limerick surrendered on 27 October 1651. The forts were abandoned. They did not stay that way. In August 1690, during the Williamite wars, King William's army arrived before the city to find the Jacobites had reoccupied and refortified the same works. The Jacobite garrison in Ireton's Fort abandoned it without a shot as the Williamites approached. When the Williamites returned the following year in 1691, the army chaplain and chronicler George Story recorded fierce fighting around the forts; Ireton's Fort and Cromwell's Fort were subsequently renamed Mackay's and Nassau's forts after the two officers who took them. The city capitulated on 3 October 1691.

Because the fort was levelled before the mid-eighteenth century and its exact position was never precisely recorded, there is nothing to see in the conventional sense. The scholar Simms, writing in 1967, placed it on the high ground of Singland Hill above the Penny Well, and the location around the Rebogue townland boundary is considered indicative rather than definitive. For anyone interested in the physical traces of seventeenth-century siege warfare, the companion site of Cromwell's Fort nearby offers a more tangible point of reference. What this particular spot offers instead is the slightly vertiginous quality of a place that was central to two major sieges, occupied, abandoned, renamed, and fought over across four decades, before being quietly ploughed back into the hill as though none of it had happened.