It was the climax of a four-year period, starting in 213, when Caracalla pursued a lengthy campaign in central and eastern Europe and the Near East.[3] After intervening to overthrow rulers in client kingdoms adjoining Parthia, he invaded in 216 using an abortive wedding proposal to the Parthian king's daughter as a casus belli. His forces carried out a campaign of massacres in the northern regions of the Parthian Empire before withdrawing to Asia Minor, where he was assassinated in April 217. The war was ended the following year after a heavy battle at Nisibis, with the Romans paying a huge sum of war reparations to the Parthians.