the frontier areas, but those were rapidly broken by Toghan's armies. It was in that episode that his loyal servant, Yết Kiêu, saved him from being nearly captured by the Mongols. Then he retreated to Vạn Kiếp, where he had a discussion with Emperor Trần Nhân Tông. The two agreed to call 200.000 troops from north-east areas to assemble in Vạn Kiếp. Here, on 11 February 1285, Viet navy under the direct commander of the emperor and the prince of Hưng Đạo fought a huge battle with Toghan's fleet. The Yuan fleet suffered heavily but they managed to win the battle. Emperor Trần Nhân Tông and Prince of Hưng Đạo eventually retreated to the imperial capital, Thăng Long. The Yuan forces pursued to Thăng Long and broke its defenses; however, the prince of Hưng Đạo's troops kept the enemy at bay long enough for the two emperors to escape from the city with the imperial family and the bulk of the army. The prince of Hưng Đạo and other generals escorted the royal family, staying just ahead of the Mongol army in hot pursuit. The Yuan army effectively controlled most of Annam, and surrounded the remaining Dai Viet leadership on land; however the latter fled to an island. Despite their martial success, the Yuan forces struggled greatly with heat and disease. As a result, the Yuan forces again retreated to wait until colder weather. Then Viet forces, divided into field armies commanded by the two emperors; Grand Chancellor Trần Quang Khải, Grand Prince of Chiêu Minh; Trần Nhật Duật, Prince of Chiêu Văn; and Trần Quốc Tuấn, Prince of Hưng Đạo conducted highly effective counterattacks, killing many Yuan generals like Sogetu. Third Mongol invasion In 1287, Kublai Khan this time sent one of his favorite sons, Prince Toghan to lead another invasion campaign into Đại Việt with a determination to occupy and redeem the previous defeat. The Yuan Mongol and Chinese forces formed an even larger infantry, cavalry and naval fleet with the total strength estimated at 120.000 troops according to the Mongols and 500.000 men according to the Vietnamese [but when it comes to the Mongols number, the Mongols will be more precisely since they need the precision in order to prepare food]. During the first stage of the invasion, the Mongols quickly defeated most of the Đại Việt troops that were stationed along the border. Prince Toghan's naval