Rastislav: sovereign of Moravia (846-70).

Ravenna: Byzantine city in the northern Italy. Together with the suburb of Classe, which was its port, it was a cosmopolitan naval and mercantile centre during the Early and, partly, the Middle Byzantine Eras.

rebellions: one of the most well-known rebellions incited by generals of themes was the revolt of Helladics as well as the revolt of Thomas the Slav. The first was a rebellion of Hellas' theme troops and of the Cycladic fleet and that threatened even the Capital itself (727). The second lasted three years, began at the early days of Michael΄s II Komnenos (820-829) reign and spread to the greater part of Asia Minor.

Robert Guiscard: (circa 1015-1085). Norman conqueror, one of the prime-movers in the Norman expansion into southern Italy and Sicily. From 1059, he was duke of Apulia and Calabria. His ambition for conquests in the East brought him into opposition with the Byzantine empire.

Roger II: count of Norman origin (1105-1130) and later, king of Sicily (1130-1154), he was son of the count of Sicily, Roger I (1072 -1101).

rosette: radial ornamental pattern.

rotae sericae: ornamental pattern of interconnected roundels.

rubble masonry: a method of edifice construction with stones that were not particularly carved. Characteristic of the relatively rough construction.

Rum: Persian, Arabic and Turkish denominations of the Byzantine empire.

Rus: people from Russia that appeared for the first time in written sources dated from 839. The etymology and derivation of its name is still an issue of dispute among the historians.

roll type of book, already established in ancient Greek and Roman times. It consists in a quadrangle or oblong part of paper or parchment or papyrus wrapped around a spindle and unwrapped in a vertical or horizontal direction.