The hollow, roughly five metres wide at the top and just thirty centimetres deep, runs north to east-southeast and may be the ghost of a fosse, the defensive ditch that would once have enclosed a monastic enclosure. It is an easy feature to walk past without a second glance, and yet it likely marks a place where people lived, prayed, and worked more than a thousand years ago.

Gwynn and Hadcock, writing in 1970, identified this as an early monastic site, one that probably ceased to function before the eleventh century. That puts its active life somewhere in the early medieval period, when small monastic communities of this kind were scattered across Ireland, often founded by local saints or minor ecclesiastical figures whose names have since been forgotten entirely. What makes the Ardtully site particularly telling is a detail recorded by the historian Charles Smith in 1756: he noted that stones from the monastic site had been quarried and reused in the construction of nearby Ardtully Castle. It was a common enough fate for ancient structures, their carefully cut or gathered stone too useful to leave in place, but it means that the monastery was effectively dismantled to build something else, leaving that faint curving depression as the only thing the ground still remembers.