Before moving to the North to begin a fight against the Chinese Qing invading army two hundreds year ago, King Quang Trung had an altar set up at Phu Xuan citadel to carry out the act of worship.
"We will defeat the Qing invaders and bring peace to the people. Now take a good look at two hundreds coins. I'll throw them highly into the air. If they lie with head upward, our great work will be fraught with difficulties; on the contrary, that's the token of victory," King Quang Trung said before all his troops.
Leaving the altar, he stepped down, taking the tray full of coins from the altar. He then respectfully carried it high above his head before throwing them all on the ground. All carefully looked, shouting in chorus: "The reverse side, all are in the reverse side! We will win. A great victory!"
King Quang Trung was really happy. "All my soldiers, that's the token of a victory. If we are unanimous in fighting against the Qing army, we will win, " he clearly stated.
As a result, the Tay Son insurgent army attacked and occupied the Qing army's fortifications in Khuong Thuong on the 5th of Ky Dau Luna New Year (1789). Chinese leader Sam Nghi Dong had to garrotte himself while another leader Ton Si Nghi (Sun Shi-yi) was so scared that he hastily jumped on a horse and together with a small group of soldiers retreated from Thang Long. Dong Da mound is now a Vietnam's historical monument.
"The token of victory" was actually King Quang Trung's unusual stratagem. All were superstitious at that time. They believed in God. Before carrying out the act of worship, King Quang Trung had secretly had two hundreds coins casted with both reverse sides. He used them in the ceremony to encourage his soldiers to win.
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