In 607, Empress Suiko sent a diplomatic document to China, which she wrote "the emperor of the land of the rising sun (日出處天子) sends a document to the emperor of the land of the setting sun (日沒處天子)" and began to use the title emperor externally. As early as the 7th century, the word 天皇 (which can be read either as "sumera no mikoto", divine order, or as "tennō", Heavenly Emperor, the latter being derived from a Tang Chinese term referring to the Pole star around which all other stars revolve) began to be used. The earliest use of this term is found on a wooden slat, or "mokkan", unearthed in Asuka-mura, Nara Prefecture in 1998. The slat dated back to the reign of Emperor Tenmu and Empress Jitō. The reading 'Tennō' has become the standard title for the Japanese sovereign up to the present age. The term 帝 ("mikado", Emperor) is also found in literary sources.