according to tibetan tradition, songtsen gampo became king when 13 after his father was poisoned around 618. he was the 33rd king of the yarlung dynasty. he was born in the ox year. yarlung kings usually took throne at 13. this accords with the tradition that the yarlung kings took the throne when they were 13, when they were old enough to ride a horse. if this is true, then gampo may have been born in the ox year 605 ce. the "old book of tang" confirms that he "was still a minor when he succeeded to the throne."