in 625, heraclius dispatched to the steppes his emissary, named andrew, who promised to the khagan some "staggering riches" in return for military aid. the khagan, on his part, was anxious to secure the chinese-byzantine trade along the silk route, which had been disrupted by the persians in the aftermath of the second perso-turkic war. he sent word to the emperor that "i shall take revenge on your enemies and will come with my valiant troops to your help". a unit of 1,000 horsemen fought their way through persian transcaucasia and delivered the khagan's message to the byzantine camp in anatolia.