Newcastle West or simply Newcastle (an Caisleán Nua, formerly anglicized Castlenoe) is a town in west County Limerick, Ireland. It is the largest town in the county, excluding Limerick city, and sits on the River Arra which flows into the River Deel. Newcastle West is in the middle of a great bowl-shaped valley in West Limerick, known one time as the valley of the Wild Boar, apparently due to the abundance of this animal here when the area was thickly wooded.