These words indicate that Tong Yabghu was eager to retain control of the westernmost portion of the Silk Route, as he tightened his grip of its other segments all the way east to China. In April 630 Böri Shad determined to expand his control of Transcaucasia and sent his general Chorpan Tarkhan with as little as 30,000 cavalry to invade Armenia.[19] Using a characteristic ploy of nomadic warriors, Chorpan Tarkhan ambushed and annihilated a Persian force of 10,000 dispatched by Shahrbaraz to counter the invasion.[20] The Turks knew the Sassanid response would be harsh, and so they plundered cities and withdrew their forces back to the steppes.