The subject of Volume XIX of The Light and the Dark is the history of the Byzantine Empire from 642 to 1453. The general theme of the whole series is 'dualism', in short the impact of unsolvable oppositions on historical societies; this is also the subject of this volume: unsolvable oppositions in Byzantine history, in its interior policy as well as in the relationships with the surrounding nations and with Latin Europe. The concentration on this overall theme implies that many important aspects of Byzantine history are not discussed; for these the reader must turn to the existing general histories of the Byzantine Empire. Notes with references to sources and literature can be found after each chapter. There are also a Bibliography and a General Index at the back of the book. After the Preface there is a Manual, in which the reader can find, per volume and chapter, the subjects treated in the previous eighteen volumes. At the back there is also a Chronology of the history of the Byzantine Empire 642-1453, a list of all Byzantine emperors, and one of the Emperors of the Nicaean Empire. The history of the Byzantine Empire since 642 is one of permanently losing ground, until finally hardly more remained than the capital itself. Ch. I discusses the first Byzantine losses. Although the great Arabic storm ended in 642, even after this date the Empire lost several territories. Ca. 630 the Visigoths conquered Byzantine South Spain. Egypt was lost to the Arabs in the years after 639, in a few years' time. Byzantium was weakened by problems over the imperial succession; the Coptic population of Egypt felt oppressed by the Byzantines and was, in consequence, not prepared to defend their country. The Arabs founded Cairo as the new capital. The rest of North Africa, Libya and the Maghreb, were not more stoutly defended. In a very short time after 642 the Arabs conquered Libya (Cyrenaica and Tripolitania); in 654 they conquered Rhodes, while Cyprus became a kind of no man's land between Byzantium and the Arabs. The defence of the Maghreb (Tunisia, Algeria and Morocco) was weakened by the tactless ecclesiastical policy of Byzantium and by the anti-Byzantine attitude of the Berber population. The Arab invasion began in 670; in 698 the old capital Carthage was lost. Between 700 and 709 Morocco too was conquered. In 711 the Arabs invaded Visigothic Spain and conquered it in two years. Coming from Spain, the Arabs conquered Sicily, but this became a much tougher affair for them. Palermo was occupied in 831, Syracuse in 875, but the last Byzantine strongholds only in 965. Sardinia and Malta were also occupied, but an Arab attempt to conquer Crete misfired. Ch. II is about 'Byzantium and the Balkans'. From the sixth century onward the Byzantine Balkans saw the Slavs coming, first a trickle, then a stream. The tribes established themselves in the habitats where they still live: the Croats, the Slovenes, and the Serbs. The last to arrive were the Bulgarians. Their rulers acknowledged the suzerainty of the Byzantine emperors, but managed their own affairs. Byzantium's control over the Balkans was very slender and in the end virtually non-existent. The Slavs were pagans, but became Christians mainly through the efforts of the brothers Cyrillus and Methodius. The Bulgarians were the last to convert. The hardest Balkan problem for Byzantium was the relationship with Bulgaria. The Bulgarian khans began to style themselves czar, the Caesar title of the Byzantine emperors; some of them wanted to plant their throne in Constantinople. A long series of bloody wars, with great cruelties committed on both sides, were fought between the two states. It ended only when the Turks overran the Balkans in the fifteenth century. Ch. III discusses 'The threat from the East', coming first from the Seljuq and later from the Ottoman Turks. Yet, there was also a threat from the West. Normans coming from France, conquered Sicily on the Arabs between 1061 and 1091. They also invaded South Italy, the last Byzantine possession in the West, and conquered it. Ambitious Norman kings more than once invaded the Balkans and even thought of ascending the throne in Constantinople. Finally, they always withdrew again. The Arab attacks on Constantinople definitely ended in the period 771-778. It was only late in the eleventh century that there was a threat from the east again. The Seljuq Turks began attacking Armenia during the second half of the eleventh century. When the Emperor Romanus IV attempted to throw them back, he was disastrously defeated in the Battle of Manzikert in August 1071. After this Asia Minor was almost totally conquered by the Seljuqs. The First Crusade, 1096, brought relief, because the Crusaders and the Byzantines reconquered the western half of Asia Minor. Attempts to also reconquer the eastern half misfired. A new threat arose after 1300, when the Osmanli Turks, the Ottomans, overran the Seljuq Sultanate of Rum and Byzantine Asia Minor; the last Byzantine stronghold was lost in 1390. The Ottomans had then already set foot in the Balkans with the conquest of Adrianople in 1366. During the second half of the fourteenth century, the Turks conquered all the Slav principalities on the Balkans, while the Byzantine territory in Europe shrank ever more. The end came in May 1453, when the Ottoman sultan Mohammed II conquered Constantinople, heroically defended by the last emperor, Constantine IX. Chs. IV and V discuss the always problematic east-west relationship, ch. IV its political and ch. V its ecclesiastical aspects. Since Roman times westerners and easterners did not understand and appreciate each other. After the end of the western Roman Empire in 476 the eastern half carried on as the Byzantine Empire. The Byzantine emperor considered himself as the sole ruler of Europe; the Germanic kings of the West acknowledged him as such, at least nominally. The situation became more problematic, when Charlemagne became the western emperor in 800. The Byzantine emperors finally acknowledged the western emperorship, but also found that there was one emperor too much. The Crusades did not make the situation any better. The Byzantines had thought that crusader armies would be auxiliary troops for Byzantium, but the Crusaders, fighting for their own account, founded independent crusader states in Asia Minor, Syria and Palestine. The Fourth Crusade, although destined for Palestine, ended in Constantinople, which was conquered in 1204. A Latin Empire (1204-1261) was founded in the European part of the Byzantine Empire, while a Greek Nicaean Empire was founded in Asia Minor. What divided the eastern and western Churches during the Middle Ages were questions of precedence rather than theological ones. The Byzantine Church was ruled by the Patriarch of Constantinople, who nominally acknowledge the Pope's supremacy, but in practice mostly went his own way. Some Popes were very harshly treated by Byzantine emperors. For a long time the Eastern Church was torn apart by Iconoclasm. Some Byzantine emperors found that there should be no veneration of images and cruelly persecuted their opponents. A theological question that divided east and west was the insertion of the words Filioque in the creed, which the West did and the East did not. This led to a first schism, that of Photius in the ninth century. The steadily deteriorating relationship finally cause the breach of 1054, after which, although there was no real schism the Latin and Greek Churches went their own ways.