Created from the imperial retinue army, the Opsikion was the largest and most prestigious of the early themes, being located closest to Constantinople.

[2] In the 640s, however, following the disastrous defeats suffered during the first wave of the Muslim conquests, the remains of the field armies were withdrawn to Asia Minor and settled into large districts, called "themes" (themata).

[3] Thus the Opsician theme was the area where the imperial Opsikion was settled, which encompassed all of north-western Asia Minor (Mysia, Bithynia, parts of Galatia, Lydia and Paphlagonia) from the Dardanelles to the Halys River, with Ancyra as its capital.

The exact date of the theme's establishment is unknown; the earliest reference points to a creation as early as 626, but the first confirmed occurrence is in 680.

[4] Furthermore, it was not divided into tourmai, but into domesticates formed from the elite corps of the old army, such as the Optimatoi and Boukellarioi, both terms dating back to the recruitment of Gothic foederati in the 4th–6th centuries.

[8] Its prestige is further illustrated by the seals of its commanders, where it is called the "God-guarded imperial Opsikion" (θεοφύλακτον βασιλικόν ὀψίκιον; Latin: a Deo conservandum imperiale Obsequium).

[10] In 713, the Opsikian army rose up against Philippikos Bardanes (r. 711–713), the man who had overthrown and murdered Justinian, and enthroned Anastasios II (r. 713–715), only to overthrow him too in 715 and install Theodosios III (r. 715–717) in his place.

The 10th-century emperor Constantine Porphyrogennetos, in his De Thematibus, mentions further nine cities in the theme: Cotyaeum, Dorylaeum, Midaion, Apamea Myrlea, Lampsacus, Parion, Cyzicus and Abydus.