The Battle of Ngasaunggyan was fought in 1277 between Kublai Khan's Mongol Yuan Dynasty of China, and their neighbors to the south, the Pagan Empire (in present-day Burma) led by Narathihapate. The battle was initiated by Narathihapate, who invaded the Yunnan province of China. Mongol defenders soundly defeated the Pagan forces.
Hostility between the two empires had already been established by that time: when Kublai Khan had sent emissaries to regional powers of eastern Asia to demand tribute, Narathihapate refused the khan's representatives the first time they visited (in 1271), and executed them on their second visit in 1273. When Kublai Khan did not immediately respond to this insult, Narathihapate gained confidence that the Mongols would not fight him. He subsequently invaded the state of Kaungai, whose chief had recently pledged fealty to Kublai Khan. Local garrisons of Mongol troops were ordered to defend the area, and although outnumbered were able to soundly defeat the Pagan forces in battle and press into the Pagan territory of Bhamo. The presence of war elephants initially caused Mongol horses to shy in terror, but Mongol general ordered his men to shower the elephants with arrows. The wounded elephants stampeded and destroyed everything in their path. In the end, Yuan troops abandoned their offensive and returned to Chinese territory with their wounded general Khutu.
The Battle of Ngassaunggyan was the first of three decisive battles between the two empires, the others being the Battle of Bhamo in 1283 and the Battle of Pagan in 1287. By the end of these battles, the Mongols had conquered the entire Pagan empire and installed a puppet government.
In the end of 1277, Yunnan governor's son Naser ad-Din attacked Bhamo again and tried to establish postal system which had already covered Mongol Empire after defeating enemies. But deadly heat forced him to left Burma. He returned to Dadu with 12 elephants and gave them to his master Kublai khan in 1279.
The battle was later reported back to Europe by Marco Polo, who described the battle vividly in his reports. His description was presumably pieced together by accounts he heard while visiting the court of Kublai Khan.