By the 7th century, these had declined to little more than parade troops, meaning that the emperors were hard put to face the frequent revolts of the new and powerful thematic formations, especially the Opsicians, the Asian theme closest to the capital.
Within the first sixty years since its creation, it was involved in five revolts, culminating in the briefly successful rebellion and usurpation of the throne by its commander, the Count Artabasdos, in 741–743.
A career in a tagma could lead to a major command in the provincial thematic armies or a high court appointment, as promising young men had the opportunity to catch the Emperor's attention.
There is much debate as to the exact size and composition of the imperial tagmata, owing to the inaccuracy and ambiguity of the few contemporary sources (military manuals, lists of offices and Arab accounts, primarily from the ninth century) that deal with them.
[21] The largest subdivision of the tagmata was the bandon, commanded by a komēs "count", called skribōn in the Exkoubitores and tribounos "tribune" in the Noumeroi and Walls units.
The Domestic of the Schools, the head of the Scholai regiment, became gradually more and more important, eventually coming to be the most senior officer of the entire army by the end of the tenth century.
The next table gives the evolution of the theoretical establishment size of the entire imperial tagmatic force, again as calculated by Warren Treadgold: As the Byzantine Empire embarked on its campaigns of reconquest in the 10th century, the tagmata became more active, and were posted often in garrison duties in the provinces or in newly conquered territories.
[29] Many of the new tagmata were composed of foreigners, such as the Maniakalatai, formed by George Maniakes from Franks in Italy,[29] or the most famous of all tagmatic units, the 6,000-strong mercenary Varangian Guard (Τάγμα τῶν Βαραγγίων), established c. 988 by Emperor Basil II (r. 976–1025).
[31] The great conquests in the East in the 960s were secured by the creation of an array of smaller themata, in which detachments of these professional forces were based, eventually to be grouped under regional commanders with the title of doux or katepanō.
[35] Consequently, in the 11th century, the distinction between "imperial" and provincial forces largely vanished, and the term tagma was applied to any permanent formed regiment, and regional origins and identities are prominently displayed in the units' titles.