1. Historical context
After the final restoration of icons by the empress Theodora (March 843) the Byzantine Empire entered a period of political stability following the long and tumultuous Iconoclastic controversy; this allowed the Byzantines to turn anew against the Arabs on land and sea. The fact that the iconophiles wished to prove that, by ensuring God' help, Byzantium could gain effective victories over its enemies played an important role to this march of events.
The first military operation accomplished in this spirit was the campaign of Theoktistos, and one of young Michael III’s regents (842-867), against the Arabs of Crete - just one week after the Triumph of Orthodoxy, on March 18, 843. Although the campaign was initially successful, it failed to restore Crete under Byzantine rule.1 In 844, and while Theoktistos was still in Constantinople, news dispersed that the Arabs of the east, under the command of Abu Said, had invaded the Byzantine lands of Asia Minor, aided perhaps by the forces of the of Melitene Amr al-Aqta', who often helped the of Baghdad in their struggle against the Byzantines to gain control of Asia Minor. It appears that the Arabs, moving through the themes of Cappadocia, Anatolikon, Boukellarion and Opsikion had reached Bosporus, having ravaged Dorylaeum on their way2. Empress Theodora ordered Theoktistos to move immediately against the invaders in order to face this new Arab attack.
2. The battle
In 844 Theoktistos left Constantinople embarking on a new campaign against the Arabs and he finally confronted them in the area of Mavropotamos, whose precise location is disputed (it is either a tributary of the Sangarius River in Bithynia or of the Halys River in Cappadocia).3 During the fight the Byzantine forces suffered a crushing defeat, as a great number of soldiers were killed in the battlefield, while many others defected to the Arab camp. Immediately after his defeat, Theoktistos returned to Constantinople.
The outcome of the battle against the Arab invaders in the area of Mavropotamos was followed by significant losses for the Byzantine army, since the Byzantine soldiers defected to the enemy camp were added to the large number of casualties in the battlefield. Thus the somewhat bolstered morale of the soldiers following Byzantium's temporary success against the Arabs of Crete started to droop again.
The negative consequences, however, were confined to this level only, for internal problems in caliph al-Wathiq’s state (842-847) did not allow him to take advantage of his military success at Mavropotamos and vigorously pursue the war against the Byzantine Empire. For this reason, notwithstanding his advantageous position, the Arab leader entered into/proceeded to negotiations with the Byzantines, which resulted in the signing of a peace treaty in 845 and the exchange of prisoners by the river Lamos in Cilicia. This fact suspended the hostilities between the Arabs and the Byzantines in the region of Asia Minor for a long period of time.In Byzantium, the defeat at Mavropotamos had an immediate impact on the internal political scene, for after his return to Constantinople, Theoktistos accused Bardas, uncle and regent of the young emperor Michael III, of being responsible for the defection of his soldiers to the Arabs. With this argument he pressured empress Theodora to send her brother away from the Byzantine capital, even to to exile him.
1. Because of a false rumour, that Theodora was planning to proclaim a new emperor at Constantinople, Theoktistos hastened his return to the capital, while the Byzantine army, without any leadership, became easy prey to the Arabs.
2. Vasiliev A.A., Byzance et les Arabes 1: La Dynastie d'Amorium (820-876) (Corpus Bruxellense Historiae Byzantinae 1, Bruxelles 21968), p. 196, provides this itinerary of the Arab campaign, identifying it with the victorious campaign of Abu Said which is described in the Arab sources as taking place during the reign of empress Theodora (between 842 and 850, date of Abu Said's death). Belke, Κ. - Restle, M., Tabula Imperil Byzantini 4: Galatien und Lykaonien (Wien 1984), p. 67, agree with this view.
3. Vasiliev A.A., Byzance et les Arabes 1: La Dynastie d'Amorium (820-876) (Corpus Bruxellense Historiae Byzantinae 1, Bruxelles 1968), pp. 196-197; Hild, F. - Restle, M., Tabula Imperil Byzantini 2: Kappadokien (Kappadokia, Charsianon, Sebasteia und Lykandos) (Wien 1981), p. 79. Treadgold, W.T., A History of the Byzantine State and Society (Stanford 1997), p. 447, supports the first view, placing the battle in the theme of Optimaton.