According to Tibetan tradition, Songtsen Gampo was enthroned while still a minor as the thirty-third king of the Yarlung Dynasty after his father was poisoned circa 618. He is said to have been born in an unspecified Ox year and was 13 years old (12 by Western reckoning) when he took the throne. This accords with the tradition that the Yarlung kings took the throne when they were 13, and supposedly old enough to ride a horse and rule the kingdom. If these traditions are correct, he was probably born in the Ox year 605 CE. The "Old Book of Tang" notes that he "was still a minor when he succeeded to the throne."