The Vipava is a river that flows through western Slovenia and north-eastern Italy. The river is 49 kilometres (30 mi) in length, of which 45 km in Slovenia. After entering Italy it joins the Isonzo/Soča in the Municipality of Savogna d'Isonzo. This is a rare river with a delta source, formed by nine main springs. The Battle of the Frigidus was fought near the river, which was named Frigidus ('cold') by the Romans. It has a pluvial-nival regime in its upper course and a pluvial regime in its lower course.