At Tonacooleen in north Galway, a subcircular earthwork sits in the landscape in fair condition, its shape roughly 36 metres north to south and 31 metres east to west, large enough to have enclosed a substantial farmstead or the residence of a local landowner of some standing in early medieval Ireland.

A rath is an earthen ringfort, the most common monument type in the Irish countryside, typically dating from roughly the fifth to the twelfth century. Most were the enclosed farmsteads of free farmers or minor lords, their banks and ditches marking a boundary between the domestic interior and the wider world. This one at Tonacooleen was built with two concentric banks and a fosse, the fosse being the ditch cut between the two banks, which would have added both to the defensive impression and the drainage of the interior. The inner bank is best preserved from the north-west around through the north to the north-east, and again at the south-east; elsewhere the enclosing element has reduced to a scarp, a slope in the ground rather than a proper standing bank. The outer bank and fosse survive only at the south-east. What is also notable is the relationship of this site to its immediate surroundings: another ringfort lies immediately to its north, making this part of Tonacooleen an unusually dense concentration of early medieval enclosure.