Few borders throughout human history have possessed such significance, over the course of so many centuries, as that which lay between the Islamic and Eastern Roman (Byzantine) worlds – or, viewed through the religious eyes of the Middle Ages, the Muslim oecumene and Christendom. This border first formed with the rise of Islam in the mid-seventh century, and vanished only in 1453, at the final resolution of the long struggle with the victory of the Islamic side in the Muslim conquest of Constantinople and the end of the Eastern Roman Empire. But it is neither temporal perdurance nor symbolism alone that imparts significance to this particular border; for one of the more salient and original features of this border was its long-lasting import, not merely in its political or military aspects, and its dimension of inter-civilisational struggle, but also in its religious and cultural effect upon the development of the internal life of both civilisations. It captured the imagination and the attention of the cultures on either side of the border in a way that, for instance, the contemporaneous Islamic border with the sub-Saharan African world did not.

As with all such borders, moreover, the Islamic–Byzantine frontier not only divided the two rival civilisations, but also brought them into contact with each other, to their mutual enrichment. One of the more neglected aspects of the history of the Islamic–Byzantine border is the ways in which it influenced unique internal developments within each of the surrounding civilisations, in the period from the inception of the Islamic–Byzantine border in the seventh century through to the end of the age of the Crusades, with the fall of the last Crusader polity in the Levant shortly before the year ad 1300.

Historical Overview

The era of Late Antiquity which preceded the rise of the Islamic Empire and the Islamic–Byzantine border was formed by three elements: (1) Diocletian's administrative division of the Roman Empire in the third century into Eastern and Western empires, and the rise of the Sasanian Empire in the Middle East; (2) the Christianisation of the Roman Empire in the fourth century, and the hammering out over the course of the succeeding centuries, through religious controversies and councils, of the major Christian doctrines, both Orthodox and dissenting;