Early 4th cent.: The early Byzantine army is divided into strike units and frontier units (limitanei).
6th cent.: Gradual decrease of the military importance of the frontier units.
634: The Arabs begin launching raids in Asia Minor.
Late 7th cent. The eastern frontier is stabilized. The Byzantines develop their defensive system; creation of the first kleisourai. The term «akritai» with a military meaning is probably beginning to occur by now.
Mid-9nd cent.: Large-scale, state-organized Arab raids cease. The small-scale raids continue, affecting only localites.
Late 9th cent. Armenian populations are settle along the eastern border. Gradual development of an internal defensive zone manned by Armenians.
960s: The great Byzantine counteroffensive begins in Cilicia and Syria. The Arab raids cease.
Late 10th cent. The new, more extensive eastern frontier of the Byzantine Empire become stable. The strategic importance of the «akritai» diminishes.
11th cent.: Decline of the defence of the east border. Asia Minor is conquered by the Seljuks.
1160s: The theme of Neokastra is created. The Byzantine defensive line in Asia Minor is fully reconstituted.
1204-1261: Reorganisation of acritic populations in the Empire of Nicaea.
c.1262: The «akritai» of Trikkokia rebel against Michael VIII Palaiologos. Chadenos’ reforms. The «akritai» of Asia Minor become incorporated into the regular army and many are relocated to European territories.
1260s: The eastern frontier collapses.
Late 13th cent. The Byzantine defensive line in Asia Minor is fully disarranged. Almost whole of Asia Minor is captured by the Ottomans.