裴矩
In the fall of 615, when Emperor Yang was visiting Yanmen Commandery on the northern frontier, the khagan launched a surprise attack on the area, overrunning most of its Chinese settlements. Warned by the khagan's wife Princess Yicheng — a member of the imperial family who had been well treated by Empress Xiao during an earlier visit — the emperor, empress, and their entourage escaped to the commandery seat at present-day Daixian. The Turks besieged them there on September 11. Resources in seat was small. Emperor was reported to cry out of fear seeing Yuwen suggested Emperor Yang select a few thousand elite cavalry soldiers to attempt a break out, but Su Wei and Fan Zigai (樊子蓋) persuaded Emperor Yang not to attempt this. Emperor Yang put Xiao Yu and Pei Ju in charge of planning the military counteroffensive, but was only able to get the siege lifted after he followed the advice of the empress's brother Xiao Yu and sent messengers to Princess Yicheng, who was directing military affairs at the Turkic capital in her husband's absence. She falsely informed Shibi Khagan that the Turks were under attack from the north, and so the khagan lifted the siege.