As TAKECHI no Kuroto, a Manyo kajin (poet of Manyoshu (Collection of Ten Thousand Leaves)), read in his poem, 'Climbing over Mt. Shihatsu I see Kasanui Island and a simple little rowing forth to disappear,' the area was called Kasanui-jima Island in the ancient times.
万葉歌人高市黒人（たけちのくろと）が「四極山（しはつやま）うち越え見れば笠縫の島　漕ぎ隠る　棚無し小舟」と詠んだ様に、古代には、笠縫島といわれた。