Byzantine army

Just as the Byzantine Empire was a continuation of the Roman Empire, so the Byzantine army was an outgrowth of the earlier Roman structure. As with all other forces during the middle ages, there was a loss of prestige and interest in the infantry and a corresponding expansion of the importance of the cavalry. This was assisted by the introduction and development of the saddle and the stirrup in the early Dark Ages.

After reforms in the 8th century, the Byzantine army consisted of:

• The Themata, the defensive militia of the Themes,
• The Tagmata, the professional, offensive standing army, and
• The Hetaireia, the foreign or mercenary troops in the Imperial Guard and general service

The success of this model under Basil II and the subsequent shifting of resources away from training and maintaining soldiers caused a long period of atrophy and increased reliance on the Hetaireia forces, culminating in the disastrous Battle of Manzikert.

After the loss of Asia Minor to the Seljuk Turks, Byzantium was never able to raise adequate numbers of themata again.

Despite the importance the Byzantine Empire (or Ρωμαναι, as it called itself) attached to its position as the defender of true, orthodox Christianity against Muslim and Catholic alike, it is worth noting that the Empire never developed or understood the concept of "Holy War." Its neighbors' concepts of Jihad and Crusade seemed to it gross perversions of scripture or simple excuses for looting and destruction. Emperors, generals and military theorists alike found war to be a failing of governance and political relations, to be avoided whenever possible. Only wars waged defensively or to avenge a wrong could in any sense be considered just, and in such cases the Byzantines felt that God would protect them.

• De re militari.org - The Society for Medieval Military History