The earliest source of a number of collects and other forms in the BCP. A sacramentary is a liturgical book which contains those parts of the rites (Daily Offices, Eucharist, and Pastoral Offices) read by the celebrant. The oldest known Roman Sacramentary is the Leonine or Verona Sacramentary which exists in a manuscript from about 600. It contains materials from the fifth and sixth centuries. The next oldest is the so-called Gelasian Sacramentary which exists in an eighth-century manuscript but represents a time slightly later than the Leonine or Verona Sacramentary. It was for a long time incorrectly attributed to Pope Gelasius I (d. 496).
Glossary definitions provided courtesy of Church Publishing Incorporated, New York, NY,(All Rights reserved) from "An Episcopal Dictionary of the Church, A User Friendly Reference for Episcopalians," Don S. Armentrout and Robert Boak Slocum, editors.