The field, tellingly labelled ‘Castle Field’ on the 1840 Ordnance Survey map, likely contains the remnants of Annaghrostie Castle and its protective bawn. Though some suggest an orchard 90 metres west-northwest of Ashfort Cottage could be an alternative location for the castle’s defensive walls, the earthworks in Castle Field remain the most probable candidate for this forgotten fortification.

The castle’s history stretches back to at least 1542, when records show it was held by Tege O’Brene, with Brian Duff taking possession by 1584. By 1600, Nicholas Stritch owned half of what was then described as the castle and surrounding wall or bawn of Annagh Rosin. The site’s various spellings; Anaroche, Annagh Rosin, Anagh Irestie; reflect centuries of linguistic evolution and the challenges of anglicising Irish place names. A 1609 perambulation deed mentions both a ford and brook at Anagh Irestie, suggesting the strategic importance of this waterside location.

The castle’s later history saw it incorporated into the parish of Mungret by 1657, positioned near a stream opposite Greenmount according to contemporary surveys. Edward Rolleston received confirmation of ownership in 1667, marking one of the last documented references to the structure. Today, only subtle traces in the landscape hint at this once-important fortification, its stones likely repurposed for local building projects whilst its earthworks slowly merge back into the Irish countryside.