Beyond its tense relationship with Western Europe, the Byzantine Empire, located astride Europe and Asia, also interacted intensively with its other neighbors. On a political and military level, Byzantium continued the long-term Roman struggle with the Persian Empire. That persisting conflict weakened both of them and was one factor in the remarkable success of Arab armies as they poured out of Arabia in the seventh century. Although Persia quickly became part of the Islamic world, Byzantium held out, even as it lost considerable territory to the Arabs. A Byzantine military innovation, known as “Greek fire”—a potent and flammable combination of oil, sulfur, and lime that was launched from bronze tubes—helped to hold off the Arabs. It operated something like a flamethrower and subsequently passed into Arab and Chinese arsenals as well. Byzantium’s ability to defend its core regions delayed for many centuries the Islamic advance into southeastern Europe, which finally occurred at the hands of the Turkish Ottoman Empire in the fifteenth and sixteenth centuries.

Economically, the Byzantine Empire was a central player in the long-distance trade of Eurasia, with commercial links to Western Europe, Russia, Central Asia, the Islamic world, and China. Its gold coin, the bezant, was a widely used currency in the Mediterranean basin for more than 500 years, and wearing such coins as pendants was a high-status symbol in the less developed kingdoms of Western Europe.13 The luxurious products of Byzantine craftspeople—jewelry, gemstones, silver and gold work, linen and woolen textiles, purple dyes—were much in demand. Its silk industry, based on Chinese technology, supplied much of the Mediterranean basin with this precious fabric.

The cultural influence of Byzantium was likewise significant. Preserving much of ancient Greek learning, the Byzantine Empire transmitted this classical heritage to the Islamic world as well as to the Christian West. In both places, it had an immensely stimulating impact among scientists, philosophers, theologians, and other intellectuals. Some saw it as an aid to faith and to an understanding of the world, while others feared it as impious and distracting. (See “Reason and Faith” later in this chapter.)

Byzantine religious culture also spread widely among Slavic-speaking peoples in the Balkans and Russia. As lands to the south and the east were overtaken by Islam, Byzantium looked to the north. By the early eleventh century, steady military pressure had brought many of the Balkan Slavic peoples, especially the Bulgars, under Byzantine control. Christianity and literacy accompanied this Byzantine offensive. Already in the ninth century, two Byzantine missionaries, Cyril and Methodius, had developed an alphabet, based on Greek letters, with which Slavic languages could be written. This Cyrillic script made it possible to translate the Bible and other religious literature into these languages and greatly aided the process of conversion.