Another son of Duke Xian was Duke Wen of Jin (636-628), who spent 19 years exile in various courts. He came to the throne in 636 escorted by the troops of his father-in-law, Duke Mu of Qin. Duke Wen quickly established himself as an independent ruler by driving the Di barbarians west of the Yellow River. In 635BC he supported King Xiang of Zhou against a rival and was rewarded with lands near the royal capital. In 633BC, he confronted the rising power of the southern state of Chu which was then besieging Song. Instead of directly assisting Song, he attacked two vassals of Chu, Cao and Wei. The following year, he formed a military alliance with Qin, Qi and Song that defeated Chu at the Battle of Chengpu, perhaps the largest battle in the Spring and Autumn period. Shortly after the battle, he held an interstate conference at Jitu (踐土) with King Xiang of Zhou and the rulers of six other states. He affirmed the lords' loyalty and received from the King the title of "ba" or hegemon. At some point there was a war with Qin which ended in peace. Duke Wen erected monuments to the fallen on both sides. The Chinese proverb "The Friendship of Qin and Jin", meaning an unbreakable bond, dates from this period.