These roughly circular enclosures were the farmsteads of early medieval Ireland, typically dating from around the sixth to the twelfth century, and they dot the landscape in their thousands. What makes any individual example worth pausing over is often the quality of its survival, its setting, or the quiet fact that it has simply endured in a county where the land has been worked and reworked across centuries of considerable hardship.

The cashel form was particularly suited to the west of Ireland, where stone lay close to the surface and timber was scarce. Builders would raise a substantial circular wall, sometimes several metres thick, to enclose a family's dwelling, outbuildings, and livestock. The term cashel derives from the Irish caiseal, and these structures served both practical and social functions, the enclosing wall marking out not just a physical boundary but a household's standing in the local order. Mayo has a notable concentration of such sites, shaped in part by the rocky, thin-soiled terrain that made stone construction the logical choice for generations of farmers whose names are now largely unrecoverable.