The Parthians launched several assaults with little result until night fell, when both sides withdrew to their camps. The second day was a repeat of the first, but on the third day the Parthians, using their greater numbers and superior mobility, tried to outflank the Roman line. The Romans responded by abandoning their customary "deep" formation in several lines (the triplex acies)[10] and extended their front.[11] Thus, by also maneuvering their cavalry and light troops to protect the wings, they avoided being outflanked and encircled.[12]