The officials told the duke that the northern Rong and Di tribes frequently attacked Jin such that the princes were needed to defend their territory.[citation needed] Duke Xian then sent Prince Shensheng to defend Quwo.[1] Duke Xian also sent Chong'er to defend the city of Pu (蒲), northwest of modern Xi County in Shanxi, and Yiwu to Erqu (二屈), modern Ji County in Shanxi.