Eiscir Riada

The Eiscir Riada extends roughly 200 kilometers from Dublin on Ireland's east coast to Galway on the west coast, forming a natural corridor across the center of the island. This raised gravel ridge cuts through the midlands and provides a continuous line of relatively dry, elevated ground.

It was formed as a deposit of sediment left by meltwater flowing through tunnels beneath a glacier during the last Ice Age. When the glacier eventually retreated, the sediment that had filled these subglacial channels remained as long, winding raised ridges standing above the surrounding landscape.

Because its raised gravel ridge offered drier, firmer ground than the surrounding bogs and wetlands, it served as a primary travel and settlement route across central Ireland for thousands of years. Early medieval Ireland was conceptually divided along this line into two halves: Leth Cuinn (Conn's half) to the north and Leth Moga (Mug's half) to the south.

Sections of the esker are visible and accessible in counties such as Offaly, Westmeath, and Kildare, where walking trails pass along or near the ridge. Modern roads including sections of the N6 between Dublin and Galway broadly follow the same corridor that the esker established.