I’ve already built a number of threads about this topic in the past, but rather than digging them up again (they’re probably closed anyway), I decided to build yet another one.
So yeah, I’d like to introduce here the Roman Mass as it would have been during the 7th-9th centuries. Our main texts for the moment are:
Ordo Romanus I: According to the Catholic Encyclopedia article, “[t]he first of these Ordines Romani, describing the ceremonies of a solemn Mass celebrated by the pope himself or his deputy, is the most valuable, as it is also one of the most ancient. Modern opinion inclines to the belief that the early part of it (numbers 1-21) really represents in substance the usages of a stational Mass in the time of Pope Gregory the Great …], but there are also, undoubtedly, in our present text adjustments and additions which must be attributed to the end of the seventh century.” Internal evidence suggests that it was compiled about AD 700 by someone with an intimate knowledge of the organization of the papal court. The oldest manuscript (Saint-Gall 614) dates from about 850; later manuscripts make numerous additions to the text, which reflect minor developments of the ceremonial.
Ordo of St. Amand, aka Ordo Romanus IV: An Ordo Romanus found in a late 8th-early 9th century manuscript (Cod. Parisinus 974), which was originally from the abbey of Saint Amand in modern Saint-Amand-les-Eaux. The ordo is largely based based on Ordo I, although it incorporates some Frankish practice.