Turma

[3] As in earlier times, these men were drawn from among the 18 centuriae of the equestrian order, the wealthiest classes of the Roman people, who could afford to provide for the horse and its equipment themselves.

[4][5] Individual turmae of camel-riders (dromedarii) also appear among cohortes equitatae in the Middle East, and Emperor Trajan (r. 98–117) established the first all-camel cavalry unit, the Ala I Ulpia dromedariorum Palmyrenorum.

[4][7] The exact size of the turma under the Principate, however, is unclear: 30 men was the norm in the Republican army and apparently in the cohortes equitatae, but not for the alae.

[12] Traces of this structure also apparently survived in the 6th-century East Roman army: in the late-6th-century Strategikon of Maurice, the cavalry files are led by a dekarchos (Greek: δέκαρχος, "leader of ten").

[12] In the 7th century, as a result of the crisis caused by the early Muslim conquests, the Byzantine military and administrative system was reformed: the old late Roman division between military and civil administration was abandoned, and the remains of the East Roman army's field armies were settled in great districts, the themata, that were named after them.

[14] The army of each thema (except for the Optimatoi) was divided into two to four tourmai,[14] and each tourma further into a number of moirai (μοίραι) or droungoi (δροῦγγοι), which in turn were composed of several banda (singular: bandon, βάνδον, from Latin: bandum, "banner").

[15] This division was carried through to the territorial administration of each thema: tourmai and banda (but not the moirai/droungoi) were identified with clearly defined districts which served as their garrison and recruitment areas.

[16] In his Taktika, Emperor Leo VI the Wise (r. 886–912) presents an idealized thema as consisting of three tourmai, each divided into three droungoi, etc.

[24] In some sources, the earlier term merarchēs (μεράρχης, "commander of a meros, division"), which occupied a similar hierarchical position in the 6th–7th centuries,[25] is used interchangeably with tourmarchēs.

Bury and John Haldon that the latter was a distinct post, held by the tourmarchēs attached to the governing stratēgos of each thema and residing at the thematic capital.