Prince of Yan
In December 1398, to prevent what he believed was a potential attack from his uncle Zhu Di the Prince of Yan, the Jianwen Emperor had appointed several imperial staff to Beiping (present day Beijing) where Zhu Di was stationed. In response, Zhu Di pretended to be ill while preparing for the anticipated war. However, the conspiracy was reported to the imperial staff in Beiping by one of the staff in Yan court. As a result, the arrest for the Prince of Yan was ordered by the imperial court. Zhang Xin, one of the imperial staff, decided to leak the imperial order to the Prince of Yan. To prepare for the imminent arrest, Zhu Di ordered his general Zhang Yu to gather 800 men to patrol the Yan residence in Beiping.