In 988, Basil II requested military assistance from Vladimir I of Kiev to help defend his throne. In compliance with the treaty made by his father after the Siege of Dorostolon (971), Vladimir sent 6,000 men to Basil. Vladimir took the opportunity to rid himself of his most unruly warriors which in any case he was unable to pay. This is the presumptive date for the formal, permanent institution of an elite guard. In exchange for the warriors, Vladimir was given Basil's sister, Anna, in marriage. Vladimir also agreed to convert to Christianity and to bring his people into the Christian faith.