Protostrator

The title means "first stratōr", reflecting the office's initial nature as chief of the imperial order (taxis) of the stratores (στράτορες, "grooms"), who formed a schola stratorum, as attested for staff of the praetorian prefect of Africa in the 6th century.

[5] The imperial prōtostratōr had a prominent place in public ceremonies, riding beside the emperor on processions (along with his superior, the Count of the Stable) or during the hunt.

[6][7] In the 9th–11th centuries, his subordinates included the [basilikoi] stratores ("imperial grooms"), the armophylakes (ὰρμοφύλακες, "keepers of the armaments" or possibly "of the chariots", from armatophylakes, according to Nikolaos Oikonomides), and three stablokomētes (σταβλοκόμητες, "stable counts"), one "of the City" (σταβλοκόμης τῆς πόλεως, stablokomēs tēs poleōs, i.e. of Constantinople) and two others, probably of the great imperial stables at Malagina.

Thus in c. 1042 Romanos Skleros, the brother of the favourite mistress of Emperor Constantine IX Monomachos (r. 1042–1054), was raised to the rank of magistros as well as the posts of prōtostratōr and doux of Antioch.

[9] During the Komnenian period (1081–1185), the post rose further in the court hierarchy, so that the historian Nikephoros Bryennios the Younger was able to remark that "this office has always been important to the emperors and was conferred on the highest personages",[10] while the 12th-century historian Zonaras, influenced by current usage, writes, referring to the conferment of the post to Basil the Macedonian, that "this dignity was that of distinguished persons and relatives of the emperors".

[16] The title is also attested in the medieval Kingdom of Georgia, where it was held by the duke (eristavi) of Svaneti, Iovane Vardanisdze, under King David IV (r. 1089–1125).