In 606/607, the Turks invaded eastern Persia with a large number of men, but were defeated in the first battle near the fort of Tus in Khorasan by a force of 2,000 Aswaran (elite heavy cavalry). Having lost this battle, the Turks and Hephthalites requested reinforcements from the Khagan. Sebeos exaggerates that 300,000 troops were sent to reinforce the invading army.