THERE SHOULD NOT be any doubt about the fact that the territorial expansion of the Arabs was particularly heavy during the two first centuries after Muhammad and the foundation of the caliphate. In the east the Arabs reached the borders of India; in the west they reached Spain and the realm of the Franks; only in the north were they stopped very soon after the first wave of attacks. The borderline between Syria and Mesopotamia on the one side and Byzantine Asia Minor on the other was the end of Arab expansion for centuries-the mountain chains of Taurus and Antitaurus remained insurmountable.

The Arabs tried it. For more than one and a half centuries they invaded Byzantium again and again. Four times they reached the Bosporus and twice laid siege to Constantinople, each time without success? There were invasions of Asia Minor almost every year, in some years even two or three. Although these invasions were not always large campaigns, but very often plundering raids on a rather small scale, they meant war, and fighting, and the danger of being captured or killed. One should wonder how the Arabs and the Byzantines managed these exertions of strength for decades. What role did the fighting actually play?

This article, looking into the examples of Theophanes and al- Ṭabarī respectively, is going to dwell upon the following questions: How did the Arab and Byzantine chroniclers deal with the constant fighting between the two sides lasting for centuries? Which kind of material did they use? Were there mutual influences? Are their chronicles purely factual or entirely or sporadically-literarily revised? The fact that the investigation will focus more on Theophanes than on al-Ṭabarī results from the author's differing competence in the two fields and has unfortunately been unavoidable. Similarly, it goes without saying that such a complex subject cannot sufficiently be dealt with in an article like this. But this has of course not been the goal of the study-if it leads somebody else to further treatment of the subject, its main purpose will have been achieved.

It is generally known that Theophanes used oriental sources for his chronicle. This has been proved for Syrian sources by the Greek transcriptions of Arabic names as well as by the pieces of information about events inside the caliphate.