Early 4^th cent.: The early Byzantine army is divided into strike units and frontier units (limitanei).

6^th cent.: Gradual decrease of the military importance of the frontier units.

634: The Arabs begin launching raids in Asia Minor.

Late 7^th 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-9^nd cent.: Large-scale, state-organized Arab raids cease. The small-scale raids continue, affecting only localites.

Late 9^th 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 10^th cent. The new, more extensive eastern frontier of the Byzantine Empire become stable. The strategic importance of the «akritai» diminishes.

11^th 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.