Writing in the Ryukyu Kingdom used various writing conventions, all of which were markedly different from spoken registers. A unique feature of Ryukyu's writing conventions is that in the Old Ryukyu period (1187–1609), it developed a predominantly kana writing convention that was based on sōrō-style Written Japanese but exhibited heavy Okinawan influence. After the Japanese conquest by Satsuma Domain in 1609, however, this style of writing was replaced by standard sōrō-style Japanese that was written predominantly with kanji. Other than that, Okinawan features were confined to the recordings of songs to sing, poems to read aloud, and plays to perform verbally, and did not have an autonomous status as literary writing. Instead, the Yukatchu class of the kingdom was aligned with the literary tradition of mainland Japan that was established during the Heian period.