榆林市
In 607, while Emperor Yang was conducting a tour of the northern border, he arrived at Yulin Commandery (榆林, roughly modern Yulin, Shaanxi). Yuwen Shu's sons Yuwen Huaji and Yuwen Zhiji (宇文智及), who were mid-level officials in Emperor Yang's government, secretly conducted forbidden trade with Tujue. Emperor Yang was incensed and ordered that they be executed, but at the last minute spared them, formally awarding them to their father as slaves.