Early in 627, the Göktürks and their Khazar allies approached the Caspian Gates at Derbent. This newly built stronghold was the only gate to the fertile land of Aghvania (modern-day Azerbaijan). Lev Gumilev observes that the lightly armed militia of Aghvania was no match against the hordes of heavy cavalry led by Tong Yabghu.[8] His troops stormed Derbent and swarmed over Aghvania, plundering it thoroughly.