 Complete the following phrase:  The childless Theodosius died in a riding accident on 28 July 450. His sister Pulcheria chose an elderly military commander Marcian as her husband without consulting with Valentinian. She allegedly acted in concern with the all-powerful Aspar who had been Marcians superior in the army. Marcian was proclaimed emperor in Constantinople in late August. On learning of Attilas plan about a military campaign in the west he stopped tribute payments to the Huns. Attila launched a massive incursion into Gaul at the head of a mixed army of Huns and subject peoples. Aetius assembled Roman, Visigothic and Burgundian troops and engaged the enemy 