That is what everybody knows.
However, what people do not know is that not all the Copper People were slain that day. Tada retained a bodyguard, an army of Copper People, who fought beside him until his death. When he was buried under the High Tumulus, his faithful bodyguard elected to stay with him, guarding him for eternity. There they stand, until this day, ordered in ranks, standing staring at the High Tumulus, waiting, waiting, waiting ...
The Copper Army is buried within the Sleeping City, beside Tada's High Tumulus. They stand in beaten earth trenches, covered with 20 feet of earth, which is covered again by the buildings of the Sleeping City. Each member of the Copper Army is a large human-like statue, made of Copper, standing around 6 and a half feet tall, wearing archaic copper scale mail armour, and carrying double-headed axes, one handed axes, shields and throwing axes. Nobody knows they are there. Nobody, that is, except a small number of Oasis Folk Priests, who know stories about the Copper Army. What are they waiting for? To be awakened. How can they be awakened? By a Trumpeter of the Copper Army. Where are the trumpeters of the Copper Army? Buried with the Copper Army. So, they can never be awakened. Or can they? That is what makes the Hero Wars.