Clonmacnoise Monastery is situated on the River Shannon south of the town of Athlone.
It was founded in 544 by St. Ciarán in the ancient territory of Ui Maine.
It was strategically located, at a point where the East-West land route crossed the River Shannon.
By the 9th century, it had become a major centre of religion, learning, craftsmanship and trade.
It was one of the most famous monasteries in Ireland and was visited by scholars from all over Europe.
Until the 9th century, it had close associations with the kings of Connacht.
From the 9th to 11th century, it was allied with the kings of Meath.
Many of the high kings of Tara and Connacht were buried here.
Reference: Wikipedia.