The Esker Riada or Sli Mhor ('important routeway') is a raised platform running from east to west Ireland. It was used as a transport route for people travelling from Dublin to Galway. The geographical term 'esker' is derived from the Irish word 'eiscir' meaning sand or gravel hill. It was formed in the ice age in streams under the melting ice-cap. The monastic settlement of Clonmacnoise is well situated as people living there could travel from east to west and then anywhere along the Shannon. The section of the esker to the east of the monastery is still known as the 'Pilgrim's Road'. The midlands are full of eskers of varying heights and widths. Since the area around is relatively flat there is a great view from the tops of these hills. For this reason the Esker Riada became the main thouroughfare in Ancient Ireland. This would not begin to happen for another 10,000 years when people first arrived in Ireland. They arrived by foot across the then landbridge between England and Ireland around 8,000 or 7,000 BC. It was only as the Ice Age ended that sea levels rose making Ireland a seperate land mass.