Tian Chengsi
In 779, Emperor Daizong died and was succeeded by his son Emperor Dezong. Shortly thereafter, Ma Sui was made the acting military governor of Hedong Circuit and the mayor of Taiyuan Municipality. Hedong Circuit had recently (in 778) suffered a major defeat against Huige forces, and its army was weak at the time. Ma carried new recruitment for cavalry soldiers from the rank of the officers' horse carers, built new battle wagons, and conducted rounds of battle training, thus rebuilding the Hedong Army within the span of a year. In 781, he was at Chang'an to pay homage to Emperor Dezong, when he warned Emperor Dezong that Tian Yue, who had succeeded Tian Chengsi as the military governor of Weibo Circuit (魏博, headquartered in modern Handan) in 779 and taken a conciliatory and submissive posture toward the imperial government, would nevertheless rebel eventually and that precautions needed to be taken.