With the Yuan dynasty crumbling, competing rebel groups began fighting for control of the country and thus the right to establish a new dynasty. In 1363, Zhu Yuanzhang eliminated his archrival and leader of the rebel Han faction, Chen Youliang, in the Battle of Lake Poyang, arguably the largest naval battle in history. Known for its ambitious use of fire ships, Zhu's force of 200,000 Ming sailors were able to defeat a Han rebel force over triple their size, claimed to be 650,000-strong. The victory destroyed the last opposing rebel faction, leaving Zhu Yuanzhang in uncontested control of the bountiful Yangtze River Valley and cementing his power in the south. After the dynastic head of the Red Turbans suspiciously died in 1367 while a guest of Zhu, there was no one left who was remotely capable of contesting his march to the throne, and he made his imperial ambitions known by sending an army toward the Yuan capital Dadu (present-day Beijing) in 1368. The last Yuan emperor fled north to the upper capital Shangdu, and Zhu declared the founding of the Ming dynasty after razing the Yuan palaces in Dadu to the ground; the city was renamed Beiping in the same year. Zhu Yuanzhang took Hongwu, or "Vastly Martial", as his era name.