Work on the mausoleum began soon after Emperor Qin ascended the throne in 246 BC when he was still aged 13, although its full-scale construction only started after he had conquered the six other major states and unified China in 221 BC. The source of the account of the construction of the mausoleum and its description came from Sima Qian in chapter six of his "Records of the Grand Historian", which contains the biography of Qin Shi Huang: