The Eiscir Riata is a system of eskers (glacial ridges) that runs across the midlands of Ireland from east to west, dividing the island into two parts of roughly equal size. The esker system formed at the end of the Midlandian glaciation during the dissolution of its ice sheets at around 15,000 b.c.e. Meltwater from the glacier, often transporting massive quantities of sediment during deglaciation, formed tunnels beneath the ice. Changes in the amount of flowing water could lead to an increase in the deposition of sediment, choking a section of tunnel. When the ice melted, a ridge of sand and gravel from the tunnel would emerge as an esker, which can run across the countryside over several kilometers.
In protohistory the Eiscir Riata was used to divide the island between the kings Conn Céadchathach and Mógh Nuadhat in the wake of the battle of Magh Léna, an event attributed to the early second century c.e. Conn ruled the northern territory (Leath Cuinn), and Mógh was given the southern lands (Leath Mógha). Apart from this possible use as a territorial division, the well-drained glacial ridge was also employed as a routeway for travelers across the boggy land of central Ireland. Starting in the east near Dublin and extending to Clarinbridge in County Galway, the Slighe Mhór (the Great Road) ran along the Eiscir Riata as one of ancient Ireland's five great roadways.
The importance of the Eiscir Riata to travellers is further emphasized by the establishment of a number of early Christian ecclesiastical sites along its length, including Durrow and Clonmacnoise, both in County Offaly. These monasteries needed easy access to good communication networks; Clonmacnoise, for example, was particularly well sited because it was located at a point where the river Shannon cut through the Eiscir Riata. The monastery thus stood at a major crossroads in the middle of Ireland.
SEE ALSO Landscape and Settlement
Hogan, Edmund. Onomasticon Goedelicum Locorum et Tribuum Hiberniae et Scotiae: An Index, with Identifications, to the Gaelic Names of Places and Tribes. 1910.
King, A. Heather, ed. Clonmacnoise Studies. Vol. 1, Seminar Papers 1994. 1998.
Ó Lochlainn, Colm. "Roadways in Ancient Ireland." In Essays and Studies Presented to Professor Eoin MacNeill on the Occasion of His Seventieth Birthday, edited by John Ryan. 1940.
Eileen M. Murphy