 While general Shahin Vahmanzadegan was sent to stop Heraclius with 50,000 men, Shahrbaraz was given command of a smaller army and ordered to slip by Heraclius' flank, and march for Chalcedon, a Persian base across the Bosporus from Constantinople.Khosrau II also made contact with the Khagan of the Avars to allow for a coordinated attack on Constantinople, the Persians on the Asiatic side, and the Avars from the European side.The Avar army approached Constantinople from Thrace and destroyed the Aqueduct of Valens.