Rav Amram Gaon רב עמרם גאון

The community of Barcelona sent a question to Sura: how ought one to pray — the whole order, from weekdays to festivals. The answer was not a list but a book.

Seder Rav Amram gives the sequence of prayers for the whole year and accompanies it with halakhah: what is said standing, what may be omitted, where "amen" is answered, how to proceed where customs differ. That is, it is not merely the first siddur but the first siddur with an explanation of why it is arranged as it is.

Its importance lies in the scale. By the ninth century Jewish communities were scattered from Spain to Central Asia, and customs diverged. The book from Sura gave a single skeleton on top of which each community kept its own. The Ashkenazi and Sephardi rites parted later — but they parted from a common text.

The original does not survive unchanged: the manuscripts contain later insertions, and separating them out is a scholarly task of its own.