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The Hetaireia or Hetaeria (Ancient Greek: ἑταιρεία) was a term for a corps of bodyguards during the Byzantine Empire.
Hetaireia 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 professional standing army 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.
The exact origin, role, and structure of the Imperial Hetaireia are unclear. The term first appears in the early 9th century: narrative sources record its existence in 813 as a bodyguard for the emperor on campaign. John B. Bury theorized that it was the evolution of the earlier Foederati, but this supposition was rejected by John Haldon.
The bulk of the Hetaireia was apparently composed of foreigners (ethnikoi), and contemporary accounts list Khazars, Pharganoi,[a] Tourkoi (i.e. Magyars), Franks and Arabs. Hans-Joachim Kühn even refers to it as a "Byzantine Foreign Legion". For this reason, although it is frequently mentioned alongside the native Byzantine tagmata, it was always a unit apart, with its own peculiar internal structure and a different role: whereas the tagmata were the professional regiments forming the core of the Byzantine army on campaign, the Hetaireia was responsible for the protection of the emperor himself.
The Hetaireia of the middle Byzantine period was divided in several units: three or four according to the sources, distinguished by their epithets and each, at least originally, under is respective Hetaeriarch (ἑταιρειάρχης, hetaireiarchēs).
The senior unit was the "Great Hetaireia" (μεγάλη ἑταιρεία, megalē hetaireia), under the Great Hetaeriarch (megas hetaireiarchēs), who ranked as the senior of the military officials known as stratarchai and was often referred to simply as "the Hetaeriarch" (ὁ ἑταιρειάρχης) par excellence. It was a very important position in the late 9th and first half of the 10th centuries, as he was in charge of the Byzantine emperor's security, and was entrusted with delicate assignments. It is telling that the future emperor Romanos Lekapenos held this post, and was succeeded by his son Christopher Lekapenos. According to the mid-10th century De Ceremoniis, written by Emperor Constantine VII Porphyrogennetos (r. 913–959), the Great Hetaeriarch and his unit are charged with the protection of the emperor's tent on campaign, and with the security of the imperial palace, in close association with the papias of the palace.
A "Middle Hetaireia" (μέση ἑταιρεία, mesē hetaireia) is attested in sources, and the possible existence of a "Lesser Hetaireia" (μικρὰ ἑταιρεία, mikra hetaireia) is implied by the reference to Stylianos Zaoutzes as mikros hetaireiarchēs under Emperor Michael III (r. 842–867). Alternatively, the unit of the mikros hetaireiarchēs may be identical to the barbarian regiment composed of the two companies of the Chazaroi (Χαζάροι, "Khazars") and the Pharganoi (Φαργάνοι), which is called the "Third Hetaireia" (τρίτη ἑταιρεία, tritē hetaireia) in the Escorial Taktikon of circa 975. The historian Warren Treadgold estimates the total strength of the Imperial Hetaireia in the early 10th century at 1,200 men.
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. A post in the "Great Hetaireia" cost a minimum of 16 litrai of gold, a post in the "Middle Hetaireia" a minimum of ten, and in each of the Chazaroi or Pharganoi companies a minimum of seven.
As the 10th century progressed, a tendency of amalgamation of the various units into a single command becomes evident, as the "Middle Hetaireia" seems to have been placed under the Great Hetaeriarch. The importance of the Hetaireia as a bodyguard corps declined thereafter, but the unit was one of the few regiments of the middle Byzantine army to survive into the Komnenian-era army, being attested well into the reign of Emperor Manuel I Komnenos (r. 1143–1180). 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.
The post of [megas] hetaireiarchēs 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. In the Palaiologan period, it was held by members of prominent noble families.