To sell timber for ships, and iron for swords, to the Saracens, was a mortal sin in children of the Church; but such a sin was as nothing beside the infamy of kidnapping believers as slaves for infidels, who made them soldiers to fight against their God. Charlemagne and the popes after him tried to suppress the traffic, but without avail. Slaving was so lucrative that it was carried on in the streets of Rome herself,[126] and in the thirteenth century two thousand Europeans were annually disposed of in Damietta and Alexandria, from whom the Mamelukes, the finest corps of soldiers in the East, were recruited. Thus a race grew up in Italy, which differed from the people of France and Germany because of the absence of those qualities which had caused the Germans to survive when the inhabitants of the Empire decayed. The mediæval Italians prospered because they were lacking in the imagination which made the Northern peoples subservient to the miracle-worker, and among mediæval Italians the Venetians, from their exposed position, came to be the most daring, energetic, and unscrupulous. By the end of the eleventh century their fleet was so superior to the Greek, that the Emperor Alexis had to confide to them the defence of the harbour of Durazzo against Robert Guiscard. Guiscard attacked Durazzo in 1081, at the time of the revolution which immediately preceded the debasement of the Byzantine coinage; and the demonstration that Venice had already absorbed most of the carrying trade, seems to prove that, during the last half of the eleventh century, the centre of exchanges had a pronounced tendency to abandon Constantinople. Moreover, the result of the campaign showed that the Venetian navy was the strongest in the Mediterranean, and this was of vital moment to the success of the crusades twenty years later, for, without the command of the sea, the permanent occupation of Palestine would have been impossible.