THE BYZANTINES, 11/ was at length arrested forever by Charles Martel upon the plains of Tours in 732. While Mohammedanism was thus pouring into Western Europe, Constantinople formed a bar- rier on the East which it utterly failed to sur- mount. Under Constantine IV. the Arabs as- sailed the dominions of the Byzantine Empire, and in 672 the imperial city itself sustained a siege of five months. The attempt was repeated in vain for seven consecutive years, and was fol- lowed in the end by a peace of thirty years' duration, but in 717 the Arabs again subjected the capital to a futile siege, which lasted thirteen months. If they had succeeded in their first attempts, and conquered the European provinces of the Byzantine Empire, they would have been able to advance westward and unite their forces with those of their brethren who were moving north- ward out of Spain. In that event, we should have had no victory of Charles Martel to cele- brate to-day or the deliverance of the Christian world, and the probable result would have been that delineated by Gibbon : " A victorious line of march had prolonged above a thousand miles, from the Rock of Gibraltar to the banks of the Loire; the repetition of an equal space would
