Man'yōgana (万葉仮名) is an old system of writing that uses kanji purely for their phonetic values. For example, 波 was read phonetically as ハ, rather than semantically as meaning "waves". The system takes its name from its use in the Man'yōshū (万葉集).
Both katakana and hiragana are derived from man'yōgana. For example, ア derives from the left radical of 阿, while あ derives from a cursive form of 安.