The earliest existing codification of the prayerbook is the Siddur (order) drawn up by Amram Gaon of Sura about 850.
Half a century later the famous Gaon Seadiah, also of Sura, issued his Siddur, in which the rubrical matter is in Arabic. Besides the Siddur, or order for Sabbaths and general use, there is the Mahzor (cycle) for festivals and fasts.
g Y Geonim, the heads of the schools of Sura and Pumbeditha in Babylonia.
Besides the Responsa, but closely related to them, we have the lesser Halakhoth of Yehudai Gaon of Sura (8th century) and the great Halakhoth of Simeon Qayyara of Sura (not Gaon) in the 9th century.
All these writers, however, are entirely eclipsed by the commanding personality of the most famous of the Geonim, Seadiah ben Joseph (q.v.) of Sura, often called al-Fayyumi (of the Fayum in Egypt), one of the greatest representatives of Jewish learning of all times, who died in 942.