The combination is quietly telling: a site that has drawn human attention across very different periods, the prehistoric or early medieval enclosure and the later demesne landscape occupying the same modest rise of ground above Maryfort Lough and Castle Lough.

The antiquary Thomas Johnson Westropp recorded the fort in detail around 1908 to 1909, measuring it at 108 feet north to south and 130 feet overall, with a fosse and a low inner ring, each about nine feet wide, the inner bank rising to five feet. A fosse, in this context, is the external ditch that typically accompanies such earthworks, dug to reinforce the bank thrown up beside it. Westropp noted that the hill fell away southward by six feet across its length, giving the structure a slight but deliberate slope. Mapping from 1899 and 1920 depicts the enclosure as D-shaped, approximately 38 metres on its longer axis, defined by a single enclosing element. By the time Westropp visited, planting had already begun to close in around the site, and he remarked on the view it still afforded despite this, with the faint blue hills of King's County visible beyond Lough Derg, the old castle at Fortane discernible from the slopes, and three lakes laid out below. The woodland has since thickened considerably, and those views are now largely obscured. The site takes its name from a nineteenth-century Ordnance Survey map designation, 'Mary Fort', which in turn reflects the broader Maryfort townland, itself likely named in connection with Maryfort House, whose footprint survives as a faint trace in the landscape to the south.