Clonmacnoise

Many ancient sites dot the River Shannon, but Clonmacnoise is early Christian Ireland's foremost monastic settlement and, like Chartres, a royal site. The monastery was founded by St. Ciarán between 543 and 549 at a location that was not as remote as it now appears to be, near the intersection of what were then two of Ireland's most vital routes: the Shannon River, running north–south, and the Eiscir Riada, running east–west. Like Glendalough, Celtic Ireland's other great monastic site, Clonmacnoise benefited from its isolation; surrounded by bog, it's accessible only via one road or via the Shannon.