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. Ciaran 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.