Saint Ciarán founded the monastery in the ancient territory of Uí Maine at a point where the major east–west land route (Slighe Mhor) meets the River Shannon after crossing the bogs of Central Ireland known as the Esker Riada.

[3] The strategic location of the monastery helped it become a major center of religion, learning, craftsmanship and trade by the 9th century;[4] and together with Clonard it was one of the most famous places in Ireland, visited by scholars from all over Europe.

Today the site includes nine ruined churches, a castle, two round towers and a large number of carved stone crosses and cross-slabs.

Clonmacnoise (meaning 'Meadow of the Sons of Nós') is situated in County Offaly, Ireland on the River Shannon south of Athlone.

[citation needed] In 544[2] Saint Ciarán, a young man from Rathcroghan, County Roscommon, arrived at this location with seven companions.

[6] This location was particularly important because here the major east–west land route through the bogs of central Ireland along the Eiscir Riada (an esker left by the receding glaciers of the last ice age) crossed the River Shannon.

While he was there he prophesied about the future debates in the churches of Ireland about the dating of Easter and claimed that angels had visited the monastery at Clonmacnoise.

However, the saint immediately noticed and grabbed the boy by the neck, told him to open his mouth, and then blessed him, saying that he would teach the doctrine of salvation.

Although the site was based around a core of churches, crosses, graves and ecclesiastical dwellings and workshops, it would have been surrounded by the houses and streets of a larger secular community, the metalworkers, craftsmen and farmers who supported the monastic clergy and their students.

The Book of the Dun Cow, a vellum manuscript dating to the 12th century, was written here[10][11] and its main compiler, Máel Muire mac Céilechair meic Cuinn na mBocht was reputedly murdered in a Viking raid in 1106.

[citation needed] Athlone became the main trading town for the midlands of Ireland, and the most popular route for crossing the Shannon, as well as the best-defended settlement in the region.

Ireland's move from a monastic framework to a diocesan one in the twelfth century similarly diminished the site's religious standing, as it was designated the seat of a small and impoverished diocese.

[15] The site includes the ruins of a cathedral, seven churches, two round towers, three high crosses and a large collection of Early Christian grave slabs.

This led to a landmark case when a prosecution was brought against the vandal by the Crown, due to the efforts of the Royal Society of Antiquaries of Ireland.

[18] It underwent significant restoration works in the second decade of the twentieth century, when the pitch of the roof was raised and the internal space was remodelled.

Main features of the Interpretative Centre are exhibits depicting the history of Clonmacnoise and the area, archaeological artefacts (including the original stone crosses, brought indoors for preservation and display), information on the people who would have lived and worked there, and a section on the local ecology of the Shannon and the wetland bogs.

Other amenities include a theatre for audio/visual presentations, a Fáilte Ireland tourist office, gift shop, tea room, toilets and parking.

[28] It has many cup-shaped hollows, crosses, daggers, and a pair of human feet (an example of a Petrosomatoglyph) possibly connected with the inauguration of Gaelic rulers.