Pirenne, Henri: The Expansion of Islam in the Mediterranean Basin 
How could the Occident have resisted? The Franks had no fleet. The Visigothic fleet was destroyed, while the enemy was well prepared. The port of Tunis, and its arsenal, were impregnable. On all the coasts Ribat were established: semi-religious, semi-military posts, which were in touch with one another, and maintained a perpetual state of war. The Christians could do nothing against this maritime, power; the most striking proof of this being the fact that they made only one petty raid on the African coast.
It is necessary to insist upon this point, since some excellent scholars do not admit that the Musulman conquest can have produced so complete a break. They even believe that the Syrian merchants continued, as of old, to frequent Italy and Gaul in the course of the 7th and 8th centuries. It is true that Rome, in particular, extended a welcome to a number of Syrians during the first few decades that followed the conquest of their country by the Arabs. Their influence and their numbers must have been considerable, for several of them—like Sergius I (687-701) and Constantine I (708-715)—were elevated to the Papacy. From Rome a certain number of these refugees, whose prestige was assured by their knowledge of the Greek language, presently migrated northwards, taking with them the manuscripts, ivories, and jewellery with which they had provided themselves on leaving their country. The Carolingian sovereigns did not fail to employ them in the movement of literary and artistic revival which they were fostering. Charlemagne instructed some of them to revise the text of the Gospel. It was probably one of their compatriots who left at Metz a Greek text of the Laudes, which is mentioned as having been there in the 9th century.
We may see another proof of the Syrian penetration into the Occident after the 7th century in the influence of the art of Asia Minor on the development of decorative motives in the Carolingian epoch. We know, moreover, that many of the ecclesiastics of “Francia” journeyed to the East in order to worship at the Holy Places of Palestine, and that they returned bringing not only relics, but doubtless also manuscripts and church ornaments.
It is a well-known fact that Haroun-al-Raschid, anxious to obtain the assistance of Charlemagne in his conflict with the Omayyads, granted him the sepulchre of Christ,(43) and also a vague protectorate over the Holy Places.
But all these details, however interesting they may be to the historian of civilization, tells us nothing of the economic history of the age. The immigration of scholars and artists does not in any way prove the existence of commercial relations between the countries from which they came and those in which they sought refuge. Was not the 15th century, when so many learned Byzantines fled into Italy to escape the Turks, the very period when Constantinople ceased to be a great port? We must not confuse the circulation of merchandise with the movements of pilgrims, scholars and artists. The former traffic presupposed the organization of transport and the permanent exchange of imports and exports, but the latter followed the hazard of circumstances. Before we should be justified in affirming the persistence of Syrian and Oriental navigation in the Tyrrhenean Sea and the Gulf of Lyons after the 7th century, we should have to prove that Marseilles and the ports of Provence remained in communication with the Levant after this date. But the last text which we can produce in this connection is a document relating to Corbie, dated 716.(44)
According to this text the magazine of the fisc at Marseilles, or at Fos, must still have been full of spices and oil at this period: that is, of products imported from Asia and Africa. I believe, however, that this is merely an archaism. We have here a document confirming certain ancient privileges of the Abbey of Corbie; it probably reproduced earlier texts verbatim. It is, indeed, impossible that African oil can still have been imported at this time. We may assume, of course, that the cellariutn fisci was drawing upon its stocks, but in that case we have no proof of the existence of active commercial relations in 716. At all events, this is the latest mention that we have of Oriental products warehoused in the ports of Provence. For that matter, four years later the Musulmans were landing on this coast and pillaging the countryside. Marseilles was then dead. It is idle to object, in proof of its activity that pilgrims were still passing through it on their way to the East. It is a fact that such pilgrims, since they could not traverse the valley of the Danube, which was occupied by the Avars, and then by the Hungarians, must have crossed the sea. But we find, whenever it is possible to trace the itineraries followed, that the pious travellers embarked in the ports of Byzantine Italy. Saint Willibald, the future Bishop of Eichstädt, embarked in 726 at Gaeta, after crossing the Alps. Madalveus, Bishop of Verdun, going to Jerusalem about 776, embarked upon a ship sailing from Apulia to Constantinople.(45)