[1] The most important such corps was the 'Imperial Hetaireia' (βασιλική ἑταιρεία, basilikḗ hetaireía), composed chiefly of foreigners, which formed part of the Byzantine professional standing army alongside the tagmata in the 9th–12th centuries.
[2] The term hetaireia was also applied to the smaller bodyguards of thematic military commanders (strategoi), headed by a count (κόμης τῆς ἑταιρείας, kómēs tês hetaireías),[3] and from the 13th century on, it was employed in a generic sense for the armed retinues of magnates, bound by oath to their master.
[17] Alternatively, the unit of the mikros hetaireiarches may be identical to the barbarian regiment composed of the two companies of the Chazaroi (Χαζάροι, Khazars) and the Pharganoi, which is called the 'Third Hetaireia' (τρίτη ἑταιρεία, trítē hetaireía) in the Escorial Taktikon of c. 975.
[18] By the early 10th century,[21] honorary posts in the Hetaireia were prestigious appointments that could be purchased by native Byzantine officials, connected to an annual stipend (roga) paid by the imperial treasury to the holder.
[24] By this time, however, its composition had changed: in the late 11th century, Nikephoros Bryennios the Younger reports that the Hetaireia was "customarily" made up of young Byzantine nobles rather than foreigners.
[2] The post of [megas] hetaireiarches also survived, and, detached from its military duties, remained an important court position: it was held by several influential palace eunuchs in the 11th century, and by second-rank nobles and junior relatives of the Byzantine imperial family, such as George Palaiologos, in the Komnenian period.