Drumlins, those low elongated hills shaped by retreating glaciers, were frequently chosen by early medieval farmers and landholders as sites for raths, the Irish term for a ringfort, and this one at Annagh follows that pattern with some precision. What makes the choice telling is the alignment: the ridge runs northwest to southeast, and whoever built here was thinking about elevation, drainage, and visibility all at once.

The rath itself measures roughly 27 metres north to south and just over 25 metres east to west, making it a fairly typical example of the form. It is enclosed by a bank of earth and stone about seven metres wide and rising between 0.7 and 1.3 metres, with a narrow external fosse, or ditch, running around the outside. That fosse ranges from one and a half to three metres wide and up to just over a metre deep in places. A ringfort of this kind would typically have served as a farmstead enclosure during the early medieval period, roughly the fifth to twelfth centuries, with the bank and fosse offering a degree of protection for livestock and household rather than any serious military defence. On the western side of the bank there is a break, recently widened, which is thought to mark the position of the original entrance.