Completion of Gameunsa and the Manpasikjeok Flute
King Sinmun completed Gameunsa, begun by his father Munmu; the legend of the Manpasikjeok, a flute received from the dragon of the East Sea, dates from this time.

Munmu asked to be buried in the East Sea so that he could become a dragon and guard against Japanese raiders; the offshore rock Daewangam is said to be his tomb. Sinmun finished Gameunsa facing it, leaving a hollow beneath the main hall so that the dragon could come and go.
According to the Samguk yusa, Sinmun made a flute from bamboo found on a small island; when played it drove off enemies, cured illness and brought rain, and was named Manpasikjeok, "the flute that calms ten thousand waves". The story is read as an expression of strong post-unification kingship and a longing for peace.