Cao Jinyan, an archaeologist at Zhejiang University, introduces written characters that date back 5,000 years on a stone axe at a seminar in Hangzhou, Zhejiang province, on Tuesday. The characters, believed to be the earliest ever discovered, are engraved on stone axes that were excavated from the ruins of the Zhuangqiao tomb in Qunfeng village of Lindai township, Pinghu city. Han Chuanhao / Xinhua