The East Roman Empire is beset from within by Iconoclast controversy and from without by the Arab Caliphate to the east and south and the newly formed Bulgarian Empire to the north.

Leo has repaired the extensive walls of Constantinople, and has maintained peaceful relations with the Bulgarians to the north, enabling him to concentrate his military abilities against the Arab menace to Asia Minor.

When the Caliphate invades imperial territory in 739, Leo dispatches imperial forces to engage them in Phrygia.

Leo has secured the Empire's frontiers by inviting Slavic settlers into the depopulated districts and by restoring the army to efficiency.

Akroinon is a major success for the imperial forces, as it is the first large-scale victory they have scored in a pitched battle against the Arabs.

Seeing it as evidence of God's renewed favor, the victory also serves to strengthen Leo's belief in the policy of iconoclasm that he had adopted some years before.

His military efforts are supplemented by his alliances with the Khazars and the Georgians.

Leo's victory has freed Asia Minor from any immediate serious threat of Arab conquest, and it will make possible the forceful counteroffensive and reconquest of some lost territory in the subsequent reign of his son, Constantine V.

The Empire, as the largest, richest and militarily strongest state bordering the expanding Caliphate, has been the Muslims' primary enemy, aince the beginning of the Muslim conquests.

Following the disastrous Battle of Sebastopolis in 692, the imperial armies have largely confined themselves to a defensive strategy, while the Muslim armies regularly launch raids into imperially held Anatolia.

Following their failure to capture the imperial capital, Constantinople, in 717–718, the Umayyads for a time had diverted their attention elsewhere.

From 720/721, however, they had resumed these expeditions in a regular pattern: each summer one or two campaigns have been launched, sometimes accompanied by a naval attack and/or followed by winter expeditions.

These are no longer aimed at permanent conquest but rather large-scale raids, plundering and devastating the countryside and only occasionally attacking forts or major settlements.

The raids of this period are also largely confined to the central Anatolian plateau (chiefly its eastern half, Cappadocia), and only rarely reach the peripheral coastlands.

Under the more aggressive Caliph Hisham ibn Abd al-Malik, these raids have become more important and have been led by some of the Caliphate's most capable generals, including princes of the Umayyad dynasty, like Maslama ibn Abd al-Malik or Hisham's own sons Mu'awiyah, Maslama and Sulayman.

Gradually, however, the Muslim successes have become fewer, especially as their resources are drawn into the mounting conflict with the Khazars.

The raids continue, but the Arab and Byzantine chroniclers mention fewer successful captures of forts or towns.

Nevertheless, after a major victory over the Khazars in 737 had relieved them of pressure in the Caucasus, the Arabs have intensified their campaigns against the Empire: in 738 and 739, Maslama ibn Hisham has achieved a number of successes, including the capture of the town of Ancyra.

Sulayman, son of the caliph Hisham, is first attested as leading the northern summer expedition ("of the right") against imperially held Anatolia in 732, and again in 735, in 736 (this time into Armenia) and in 737, but on neither campaign does he seem to have accomplished anything of note.

In 738 however, he had sacked an imperial fortress called Sideroun ("Iron Fort") taking many prisoners, including its commander, Eustathios.

In 740, he is placed in overall charge of the exceptionally large campaign prepared for that year, which according to the chronicle of Theophanes the Confessor totaled ninety thousand men.

Two task forces are sent first, one of ten thousand lightly armed men under al-Ghamr ibn Yazid, which is to raid the western coast of Anatolia, and twenty thousand under Abdallah al-Battal and al-Malik ibn Su'aib, who follows after towards Akroinon.

The main force of some sixty thousand (the number is certainly much inflated), under Sulayman, raids Cappadocia with Tyana as their target.

Sulayman fails to take the city, and returns home after plundering the countryside.

The second task force, however, suffers a major defeat at the Battle of Akroinon, losing some two thirds of its men, as well as its commanders.

Details of the battle are not known, but the Emperor, Leo III, secures a crushing victory: both Arab commanders fall, as well as the larger part of their army.

About six thousand eight hundred resist, however, and manage to conduct an orderly retreat to …

…Synnada, where they join Sulayman.

The other two forces devastate the countryside unopposed, but fail to take any towns or forts.

In addition, the Arab invasion army suffers from severe hunger and lack of supplies before returning to Syria.

The tenth-century Arab Christian historian Agapius also records that the imperial army took twenty thousand prisoners from the invading forces.

Forced to fall back toward Damascus, the Caliphal forces leave Asia Minor to imperial control.