The Byzantine army constantly evolved throughout its history. A worthy successor to the vast mechanism set up by the Romans, its most remarkable trait was the degree of adaptability that characterised it as an institution, along with the open-minded attitude of its officers and the tactics they applied in the battlefield. Numerous military manuals, such as Maurice's Strategikon, Leo VI's Taktika, the Praecepta Militaria of Nicephorus Phocas, the Taktika of Nicephorus Uranus and the Strategikon of this parish Cecaumenus, offer us a thorough look into the way Byzantine officers thought and how they faced their enemies in each operational theatre. They had two distinct but mutually supportive mechanisms, which had been established since the eighth century: the themata, armies which were defensive in nature and whose main objective was to intercept and harass any invading army, and the tagmata, professional units trained to deliver the final blow to the enemy on pitched battle.

The army that Alexius Comnenus deployed against the Normans in 1108 was different in both structure and make-up from that which Romanus IV Diogenes had gathered for his Turkish campaigns that culminated in the battle of Manzikert in 1071. The old thematic and tagmatic units (indigenous troops that formed the backbone of the army's structure for centuries) were largely replaced by mercenaries. Alexius Comnenus depended on the hiring of large bodies of paid troops of any ethnic background for long-term military service, like the Varangian Guard (largely comprised of Anglo-Saxons after 1081), the German Nemitzi and several Frankish regiments.