. In July 803, an Abbasid army under
al-Qasim, a son of Caliph
Harun al-Rashid (), began advancing towards the Byzantine frontier. As Nikephoros had broken his foot in early May, it fell to Bardanes to lead the Byzantine army against the Arabs. He therefore ordered the thematic armies of Anatolia assembled in the Anatolic Theme. On 19 July, Bardanes was proclaimed emperor by the assembled troops of the Anatolic,
Opsician, Thracesian and
Bucellarian themes. Crucially, the
Armeniac Theme, either because of its traditional rivalry with the Anatolics, or because it had not yet joined up with the rest of the army, did not join the uprising. It has also been hypothesized that Bardanes may have participated in the suppression of the Armeniacs' revolt in 793, leaving lingering hostility towards him amongst its troops. Among the Byzantine chronicles that report on Bardanes's revolt, the 10th-century
Theophanes Continuatus and the 13th-century
Synopsis Chronike indicate that the troops were motivated chiefly by economic concerns. Nikephoros had initiated a strict budgetary policy to shore up the Empire's finances. The Emperor had revoked the exemption on inheritance tax for the soldiers, and had apparently left them unpaid for some time as well. Bardanes, on the other hand, had a good reputation in this regard, fairly dividing the booty won from the campaigns against the Arabs amongst the soldiers. For the motives of Bardanes himself, the situation is less clear. According to the Byzantine chroniclers, he accepted the acclamation only reluctantly, after vainly entreating the soldiers to allow him to leave. According to another story however, before his revolt, Bardanes, accompanied by his three principal associates,
Thomas the Slav,
Leo the Armenian and
Michael the Amorian visited a holy man at
Philomelion to learn of the prospects for the uprising. The monk correctly prophesied that his rebellion would fail, that Thomas too would begin a revolt, and that Leo and Michael would reign as emperors. Although possibly a later invention, this story may suggest that Bardanes planned his revolt beforehand. Aside from any personal ambition, Bardanes was also a member of the
landed aristocracy and a devoted
iconophile who supported Empress Irene's regime. He has therefore also been seen as the representative of the opposition by the traditional elites to Nikephoros's policies, both in the confessional area, where the Emperor maintained a carefully neutral stance towards both iconoclasts and iconophiles, and in the socio-financial sphere, where new taxes on landed property and the expropriation of ecclesiastical estates hurt their interests. Treadgold further suggested that the revolt was a reaction against Nikephoros' usurpation and aimed, at least ostensibly, at the restoration of Irene. However, her death at
Lesbos on 8 August deprived the rebels of any claim to legitimacy. The revolt probably took place at
Amorion, the capital of the Anatolic Theme. From there, the rebel army, comprising almost half of the Empire's available military forces, marched north and west, following the military road to
Nicomedia and then to
Chrysopolis, the town that lay across the
Bosporus from the imperial capital,
Constantinople. There, Bardanes encamped for eight days, awaiting a possible uprising against Nikephoros inside the capital in response to his own rebellion. Since this did not materialize, and the populace proved not overtly enthusiastic, he withdrew to the great army base at
Malagina. There, two of his associates, Michael the Amorian and Leo the Armenian, abandoned him, and were richly rewarded by Nikephoros for their defection: Michael became
Count of the Tent to the Emperor, and Leo was appointed commander of the regiment. This desertion further discouraged Bardanes, and, reluctant to face the loyalist army in battle, he opted for a negotiated surrender through the mediation of Joseph, the (abbot) of the Kathara monastery who had officiated at Constantine VI's second marriage. Bardanes received a letter signed by the
Patriarch Tarasios and several leading
senators which guaranteed that neither he nor his subordinates would be punished if they surrendered. As a further guarantee of good faith, Nikephoros sent his own gold cross along with the letter. Satisfied by these assurances, on 8 September Bardanes left his army and, through
Nicaea, sought refuge in the monastery of Herakleios at
Cius. From there, he embarked on a ship that took him to the island of
Prote. Taking the
monastic name Sabbas, Bardanes then entered a monastery that he had founded there in the past. ==Aftermath of the revolt==