Caliph al-Ma'mun, having brought the ‘Abbasid caliphate to its greatest heights, had kept up the pressure on the Empire in 832, with his army capturing the strategically important fortress of Loulon, and in late 832 the Caliph had begun gathering a huge army and announced that he intends to conquer and colonize Anatolia step by step, and finally subjugate the Empire by capturing Constantinople itself.

Consequently, on May 833, Abbas with the advance force marches into imperial territory and begins creating a military base at the site of Tyana.

The site has been fortified and awaits the arrival of the Caliph's army, which in early July crosses into Anatolia.

At his juncture, however, luck intervenes for Constantinople, as Ma'mun falls ill and dies on October 10, although some modern scholars speculate that his death may have been the result of a coup.

Although Abbas is Ma'mun's only son, the Caliph apparently had named his brother Abu Ishak al-Mu’tasim, a younger son of the late Harun ar-Rashid, as his heir shortly before his death.

Abbas swiftly swears allegiance to Mu'tasim, but this turn of events is not popular among the assembled army, which tries to proclaim Abbas caliph.

Abbas refuses, and manages to assuage the troops' anger.

Nevertheless, Mu'tasim's hold on the throne is still shaky, and he abandons Ma'mun's campaign; the new base at Tyana is razed, and the army returns to the Caliphate.