What is "hetaireia"

n. A unit of the Byzantine emperor's bodyguard

The Hetaireia or Hetaeria was a term for a corps of bodyguards during the Byzantine Empire. It means "the Company", echoing the ancient Macedonian Companions and the Classical Greek aristocrats who attended symposia.

The most important such corps was the imperial Hetaireia (βασιλική ἑταιρεία, basilikē hetaireia), composed chiefly of foreigners, which formed part of the Byzantine imperial guard alongside the tagmata in the 9th–12th centuries. The term hetaireia was also applied to the smaller bodyguards of thematic military commanders ( stratēgoi), headed by a count (κόμης τῆς ἑταιρείας, komēs tēs hetaireias), 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.