Crannog, Roosky, Co. Monaghan

It is only eighteen metres across, circular, and almost entirely unremarkable to the casual eye. But the erosion along its northern bank tells a different story: beneath the vegetation and accumulated centuries, a matrix of stones is visible, interspersed with timber piles between ten and twenty centimetres in diameter, set at intervals of roughly a metre and a half. This is a crannog, an artificial or partially artificial island of the kind built and inhabited in Ireland from the early medieval period onward, sometimes into the seventeenth century. The structure at Roosky belongs, it seems, to both the deep past and to a relatively recent moment of political turbulence.

A map produced by the English cartographer Richard Bartlett between 1602 and 1603 depicts two crannogs in an L-shaped lake, and for a long time this image was assumed to show a crannog in Monaghan town. Research has since suggested the correspondence is closest to Roosky Lough, whose distinctive shape, a rectangular body with a perpendicular arm extending southward from its western end, matches the Bartlett depiction far more convincingly. The lake itself has shrunk considerably since it was recorded on the Ordnance Survey six-inch map of 1834, which makes the historical image harder to read at first glance. What the Bartlett map indicates, however, is that these crannogs were occupied or re-occupied in the sixteenth and early seventeenth centuries, during a period when Roosky functioned as a power centre of the Dartry Mac Mahons, a branch of one of Monaghan's dominant Gaelic families. The site had almost certainly been in use for centuries before that. Just to the east of the crannog on the present shoreline lies a possible ringwork castle, a form of early fortification consisting of an encircling earthen bank and ditch, which suggests that the broader area around the lough carried real strategic weight for whoever controlled it.