Arik-den-ili's first victories were against his eastern neighbours (the Pre-Iranic inhabitants of what was to become Persia), Turukku and Nigimhi, and all the chiefs of the (Zagros) mountains and highlands in the broad tracts of the Gutians to subdue the nomadic tribes on Assyria's northern and eastern frontiers. The Gutians had been vassals of the Kassites who ruled in Babylon and may have acted as their agents. Nigimhi's ruler was Esini. The Assyrians had invaded and carried off their harvest and in retaliation Esini led a force into Assyria which resulted in a massacre of his forces. Arik-den-ili besieged the town of Arnuna, in which Esini was holed up. Destruction of the gate and walls forced Esini's capitulation and so he swore allegiance to his Assyrian overlord.