Abbasid invasion of 806

The Abbasid invasion of Asia Minor in 806 was the largest operation ever launched by the Abbasid Caliphate against the Byzantine Empire. The expedition was commanded in person by the Abbasid Caliph Harun al-Rashid (reigned 786–809), who wished to retaliate for the Byzantine successes in the Caliphate's frontier region in the previous year and impress Abbasid might upon the Byzantine emperor, Nikephoros I (r. 802–811). The huge Abbasid army, according to Arab sources numbering more than 135,000 men, raided across Cappadocia unopposed, capturing several towns and fortresses, most notably Herakleia, and forcing Nikephoros to seek peace in exchange for tribute. Following Harun's departure, however, Nikephoros violated the terms of the treaty and reoccupied the frontier forts he had been forced to abandon. Harun's preoccupation with a rebellion in Khurasan, and his death three years later, prohibited a reprisal on a similar scale. Moreover, the Abbasid civil war that began after 809 and the Byzantine preoccupation with the Bulgars contributed to a cessation of large-scale Arab–Byzantine conflict for two decades.

• http://en.wikipedia.org/wiki/Abbasid invasion of 806