The Byzantine army of the Komnenian era or Komnenian army was the force established by Byzantine emperor Alexios I Komnenos during the late 11th/early 12th century, and perfected by his successors John II Komnenos and Manuel I Komnenos during the 12th century. Alexios constructed a new army from the ground up, completely replacing previous forms of the Byzantine army. The Komnenian army was instrumental in the Komnenian restoration of the Byzantine Empire during the period of its existence, and was deployed in the Balkans, Italy, Hungary, Russia, Anatolia, Syria, the Holy Land and Egypt.
At the beginning of the Komnenian period in 1081, the Byzantine Empire had been reduced to the smallest territorial extent in its history. Surrounded by enemies, and financially ruined by a long period of civil war, the empire's prospects had looked grim. The state lay defenseless before internal and external threats, as the Byzantine army had been reduced to a shadow of its former self. During the 11th century, decades of peace and neglect had reduced the old thematic forces, and the military and political anarchy following the Battle of Manzikert in 1071 had destroyed the professional tagmata, the core of the Byzantine army. At Manzikert, units tracing their lineage for centuries back to the Roman Empire were wiped out, and the subsequent loss of Asia Minor deprived the Empire of its main recruiting ground. In the Balkans, at the same time, the Empire was exposed to invasions by the Norman Kingdom of Sicily, the expansionist activities of the principality of Dioclea (Duklja) and by Pecheneg raids across the Danube.