Sir Steven Runciman
Western Europe has been slow to recognize its debt to Byzantium. The emergent nations of the western empire surpassed the Greeks in material power and commercial enterprise from the 13th century onwards, but they did so behind the shield of Constantinople's walls. Byzantium bore the brunt of the Mohammedan invasions, from the Arabs to the Ottoman Turks, and served as a breakwater which enabled the West to turn the tide. There were other incalculable debts; the preservation of classical literature and Roman law; the systematic study of history, the foundation of universities and the promotion of science, the rise of monasticism and missionary activity; the evolution of religious art and architecture which left their mark not only on Italy but in the Norman West.
C. M. Woodhouse, Modern Greece, A Short History
Blocked from Europe by the impregnable walls of Constantinople and the unyielding spirit of the Emperor and his people, the armies of the Prophet were obliged to travel the entire length of the Mediterranean to the Straits of Gibraltar before they could invade the continent - thus extending their lines of communication and supply almost to breaking point and rendering impossible any permanent conquests beyond the Pyrenees. Had they captured Constantinople in the seventh century rather than the fifteenth, all Europe - and America - might be Muslim today.
John Julius Norwich, Byzantium, the Early Centuries
The following paragraph would have been omitted had an arrogant Western Christian not made disparaging remarks when I lamented the City's fall. Remember, the Latin west owes more to the Byzantine east than she would care to admit.
Again, I quote C. M. Woodhouse,
In return, the West sent to Byzantium its Crusaders and traders, between whom it is hard to distinguish for unscrupulous rapacity. It is little wonder that many Greeks accepted the Turkish conquest not only as a punishment for the heretical union of 1439, but as a merciful release from Latin domination.