Having lost the first war against Persia during the First Perso-Turkic War, 30 years earlier, the invaders sought to change their fortunes while Persia was engaged fighting the Eastern Roman (Byzantine) Empire. They 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 Savaran (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.