Piyyut (from Greek poietes — ‘poet’) is the tradition of liturgical poetry composed for insertion into the synagogue service, especially for Shabbat and the High Holidays. Flourishing from roughly 500–1000 AD, primarily in the Land of Israel and later in Babylonia and Europe, piyyut represents one of the great creative achievements of rabbinic civilization. The early paytanim (composers) — Yose ben Yose, Yannai, Eleazar ha-Kallir (~570–640 AD) — developed intricate acrostic, alphabetic, and rhyming forms that became models for all subsequent Hebrew poetry. The Ashkenazi liturgy retains many piyyutim for Rosh Hashanah and Yom Kippur. Piyyut is the bridge between biblical Hebrew poetry and medieval Hebrew literature.