The monastery of Clonmacnoise (Cluain Mhic Nóis in Irish, meaning "Meadow of the Sons of Nós") is situated in County Offaly, Ireland on the River Shannon south of Athlone.
Clonmacnoise was founded in 545 by Saint Ciarán at the point where the major east-west land route through the bogs of central Ireland along the Eiscir Riada, an esker or moraine left by the receding glaciers of the last ice age crossed the River Shannon. Saint Ciarán had been educated by Saint Diarmuid of Clonard and Saint Finian.
Shortly after his arrival, Ciarán met Diarmait mac Cerbaill who helped him build the first church — a small wooden structure and the first of many small churches to be clustered on the site. Diarmuid was to claim the title of the first Christian High King of Ireland.
Ciaran died about one year later of the yellow plague; he was in his early thirties.