 The O'Connors of Offaly, the old Gaelic rulers before colonisation and plantation in the sixteenth century, had one of their main residences here, and it was also the place of inauguration of their chiefs.Just north of the hill is a holy well dedicated to St. Patrick (signposted).The late Frank Mitchell, the celebrated geologist, preferred to give the distinction of the "navel of Ireland" not to the hill of Uisneach ( north-east of Athlone) but to the isolated hill, Croghan, which he described as a mass of volcanic rock.