The site now occupied by St. Mary's Convent and its associated schools was once a military barracks, constructed during the reign of Charles II, somewhere between 1660 and 1685. That this is known at all is largely thanks to careful reading of old maps and the work of architectural historian Harold Leask, who pieced together the sequence of uses from cartographic evidence that is, in places, frustratingly incomplete.

Leask, writing in 1941, noted that the barracks occupied what he described as 'the space within the great gap', a phrase that suggests a defined enclosure or break within the city's fabric, though the precise boundaries are not easily reconstructed today. The evidence for the building's existence is largely map-based: a French map of the period does not show the barracks at all, which may indicate it was built after the French survey was made, or simply that it was omitted. By contrast, the map of 1786 included in Ferrar's History of Limerick marks several regular blocks of buildings on the site, labelled 'Barracks, later Brewery', a small annotation that compresses a significant shift in function into just three words. The transition from military use to industrial brewing, and then eventually to religious and educational use, traces something of the broader pattern of post-Williamite Limerick, as the city's built environment was steadily reorganised across the eighteenth and nineteenth centuries.

The site sits within Limerick city and is not accessible as a heritage location in any formal sense; St. Mary's Convent and the schools occupy the ground today, and there is nothing at street level to mark the earlier uses. For anyone interested in the archaeology of Limerick's changing streetscape, the most productive approach is to consult the historical maps directly, particularly the 1786 Ferrar map, which gives the clearest surviving picture of how the barracks was laid out before it was converted and eventually replaced altogether.