ABSTRACT
In the early ninth century the imperial establishment had to reckon with two vigorous dynasties to its east and west. Both the 'Abbasids and the House of Pepin had seized power fairly recently and each was liable to adopt a belligerent stance towards Byzantium. In 806 Harlin al-Rashid, at the head of a huge army, was able quite easily to exact tribute from Nikephoros I, including three nomismata by way of poll-tax payable by the emperor. Harlin thus showed off his greatly superior forces, 'as if having subjugated the empire of the Romans' .1 Charlemagne, for his part, proved ready to intervene in areas which the Byzantine government considered to come within its dominion. In laying claim to Venice and authorizing probes along the Dalmatian coast, one of Charlemagne's aims was to press the eastern emperor into recognizing his, Charlemagne's, own imperial title.2
Successive governments demurred, but at Aachen in 812 Byzantine envoys acclaimed Charlemagne 'in their own manner, that is, in the Greek tongue, calling him emperor and basileus'.3 Thus, within the space of a few years, emperors found it politic to defer to the 'Abbasid caliph and formally to recognize a western potentate as a fellow-basileus. And they could not be sure that a major 'Abbasid-led expedition would not return. In 838 Caliph al-Mu'ta$im led a massive invasion of Asia Minor, sacking Amorion.4 The blow to the prestige of emperor Theophilos was considerable, leading him to an attempt at 'grand strategy'. He even incited the Umayyad amir of
