The Byzantine Empire was the heir to two great cultures that cradled and nurtured European civilization: Greece and Rome. Constantinople, now called Istanbul, became a center of power, culture, trade, and technology poised on the edges of Europe and Asia, and its influence was felt not only throughout Europe but the Middle East, Africa, Central Asia, and the Far East. Coins dating from the reign of Emperor Justinian I (r.527-565) have been found in southern India, and Chinese records show that the "Fulin," as the Chinese named the Byzantines, were received at court as early as 643. For nearly a thousand years, the Byzantine Empire protected Europe from Islamic powers, allowing it to pursue its own destiny, and Byzantium was a polyglot society in which a multitude of ethnic groups lived under the emperor prizing peace above war.
Of course, it wasn't an accident that Constantinople survived for so long. Since ancient times, settlements have been protected by walls, ranging from simple earth fortifications, mounds, and ditches to sophisticated structures incorporating gates and watchtowers. The globe is replete with famous walls such as that built by Hadrian in the north of England and the Great Wall of China, which spans hundreds of miles across a vast landscape. Some of the earliest evidence of defensive walling can be found in Africa, and the Bible includes references to the walls of Jericho, dating back to at least the 8th century B.C. Walls have protected great civilizations and occasionally been their downfall, and the Byzantine Empire relied on Constantinople's extensive, sophisticated walls, among the greatest engineering achievements of the ancient world and Early Middle Ages, to survive as long as it did.
The Fourth Crusade was the turning point for the Crusades; after this one, the slow decline toward the Latin Christians losing the Holy Land became inevitable.
