The D-shaped enclosure at Annahean, known locally as Doileana, sits on a slight rise in an undulating stretch of south Monaghan countryside, its grass-covered interior ringed by a low earthen bank and an overgrown scarp. Surveyors working from the 1834 Ordnance Survey six-inch map could see the full extent of the enclosure clearly enough to label it in gothic lettering, but what it actually contained, or commemorated, has never been established.

The area carries older associations. A place called Eanach Chonglais, identified with nearby Killaney, appears in the Tripartite Life of St Patrick, a medieval text generally treated as historically unreliable. According to that account, Patrick passed through here on the road between Armagh and Meath, failed entirely to convert the local population, and was fortunate to leave unharmed. Conversion, if it came at all, was presumably the work of St Ultán of Ardbraccan, who became the medieval patron of the parish, though no record of his activity in the area survives. What gives Doileana its particular character is the physical evidence found here in 1940 and again in 1984: a crude cross-slab carved with a ringed cross in relief, and two bullaun stones. Bullaun stones are boulders or slabs with one or more cup-shaped hollows ground into them, and they appear frequently at early ecclesiastical sites across Ireland, often associated with ritual or curative use. When the site was visited in 2016, none of these objects could be located, though they are thought to be somewhere within the now heavily overgrown perimeter bank, absorbed into the vegetation rather than removed.