 From 1802 to 1812 , Duyệt served as a high @-@ ranking general in the new imperial capital Huế in Annam ( central Vietnam ) . In 1812 , Emperor Gia Long appointed Duyệt as the viceroy of Gia Định . At this time , the viceroy of Gia Định held jurisdiction not only over Cochinchina ( southern Vietnam ) but also over Cambodia . 
