() of varying ranks and titles in each tagma, and 40 mandatores "messengers" for a total unit size of 4125. On campaign, every tagmatic cavalryman was accompanied by a servant. The next table gives the evolution of the theoretical establishment size of the entire imperial tagmatic force, again as calculated by Warren Treadgold: Professional regiments, 10th–11th centuries 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. In addition to the older units, a number of new and specialized units were formed to meet the demands of this more aggressive style of warfare. Michael II (r. 820–829) raised the short-lived Tessarakontarioi, a special marine unit (named after their high pay of 40 nomismata), and John I Tzimiskes (r. 969–976) created a heavy cataphract corps called the Athanatoi (, the "Immortals") after the ancient Achaemenid unit, which were revived in the late 11th century by Michael VII Doukas (r. 1071–1078). Other similar units were the Stratēlatai, likewise formed by John Tzimiskes, the short-lived Satrapai of the 970s, the Megathymoi of the 1040s or the Archontopouloi and Vestiaritai of Alexios I. Many of the new tagmata were composed of foreigners, such as the Maniakalatai, formed by George Maniakes from Franks in Italy, or the most famous of all tagmatic units, the 6,000-strong mercenary Varangian Guard (), established ca. 988 by Emperor Basil II (r. 976–1025). The reign of Basil II also saw the beginnings of a profound transformation of the Byzantine military system. In the mid-10th century, the decline in the numbers of the thematic forces and the exigencies of the new offensive strategy on the eastern border gave rise to an increasing number of provincial tagmata, permanent professional forces modelled after the imperial tagmata. 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. This strategy was effective against small-scale local threats, but the concurrent neglect of the thematic forces reduced the state's ability to respond effectively to a major invasion that succeeded in penetrating the frontier buffer zone. The decline of the part-time thematic armies and the increasing reliance on a large array