The Byzantine Empire was first known as the eastern Roman empire, when Constantine I relocated the Roman capital from Rome to Constantinople and his successor Valentinian I made the division between Western and Eastern Empire official. When barbarians sacked Rome and defeated the western armies a century later, the Byzantine Empire was the final bulwark of Roman civilization to stand against the increasing pressure from European barbarians to the north and Persia in the east. Byzantine government was based largely on that of Rome, although unlike Roman emperors a Byzantine emperor was elected by a threefold vote of the senate, the people, and the army. To govern the empire, Byzantine emperors relied on a labyrinthine system of advisors, ministries, and offices — hence the pejorative "Byzantine" today, used to describe overly hierarchical and intrigue-prone systems.
The golden age of Byzantium began when Justinian I and his brilliant wife Theodora became emperor and empress. Under their rule, the Byzantine general Belisarius undertook a series of dramatic and successful campaigns against the barbarian kingdoms that had risen in the ruins of Rome. After earning imperial favor by ruthlessly quashing a popular revolt, Belisarius successfully fought the Ostrogoths in Italy, the Persians, and various tribes in North Africa. His enormous popularity eventually caused Justinian to fear him, and he was eventually stripped of his command.
Byzantine military reform came mostly during the reign of Heraclius, the son of Africa’s imperial governor. Arriving in Constantinople to restore order after a disastrous interregnum (marred by assassination, intrigue, and civil disorder), Heraclius placed tremendous power in the hands of the army. It was also during the reign of Heraclius that Greek fire, the medieval precursor to napalm, was invented, and used extensively by Byzantine ships called dromons in battle against Persian and barbarian ships. Heraclius also ordered the army to emulate the barbarian horse archers previously employed as mercenaries; the result was the cataphract, a heavily armored cavalryman who could fight with bow, sword, or lance.
After two hundred years of defeats and erosion, during which Byzantium lost virtually all of its possessions south of Asia Minor, the ascension of Basil I to the imperial throne in 867 marked a turnaround in Byzantine military fortunes. Byzantine armies beat back the Arabs in the east and south, and despite several humiliating defeats at the hands of the Muslims, reasserted dominance over the eastern Mediterranean. Syria, along with the key city of Antioch, also came back to Byzantine control, along with Armenia and large parts of the Balkans. For 150 years, Byzantium enjoyed civil prosperity and military victory.
But new adversaries appeared where the old ones had fallen. In 1071, Byzantium suffered two catastrophic defeats — they lost their last toehold in Italy to the Normans, who had earlier sacked Constantinople during a crusade gone awry. In the east, the Ottomans broke Byzantine power in Asia Minor forever at Manzikert, and the once dominant empire was reduced to a rump state comprising Constantinople, parts of the Balkans, and a few remaining provinces in western Turkey. The heart of it, though, was now ruled by the Turks. Nonetheless, during this time, art, religion, and philosophy flourished within the walls of Constantinople. It was as if the learned men of Byzantium were unaware of the threats lurking outside. Another fateful event, the Schism of 1054, finalized the separation between the Byzantine (Eastern) and Catholic (Western) churches. This would lead to deep suspicion between the two churches, and western reluctance to assist Byzantium against the Turks years later.
Eventually Byzantium was forced to resort to bribery and compromise with the Turks and the new western powers that coveted its territory and former influence. In 1421, after a hundred years of co-existence with the Turks, the new sultan Murad II revoked all of the arrangements that had existed between the two empires. As a last resort, the Byzantine emperor begged Rome for help, but the Christian army sent to fight the Turks was utterly defeated. In 1453, the Turks assaulted Constantinople itself, and the walls that had stood for over a thousand years finally fell, marking the end of the Byzantine Empire.
In Civilization III: Conquests, the Byzantines are considered a seafaring and scientific civilization. They start the game with Bronze Working and Alphabet and are able to build the Dromon instead of the Galley.
Unique Unit: Dromon
Byzantine Dromons are a type of galley with an enhanced offensive capability, as it can let loose a hot stream of "Greek Fire". The Dromon has Lethal Sea Bombardment. The dromon was the end result of Byzantine ingenuity applied to old Greek ship designs. Powered by rowers, its primary virtue was its versatility — the wide, flat decks could be mounted with a variety of weapons. There were many classes of dromon, from light escort and reconnaissance designs to heavy warships. Dromons often included mini-forts made of wood from which marines could sally forth or fire bows, as well as catapults, rams, ballistae, and later, Greek fire launchers. These dangerous and devastating primitive flamethrowers spelled death to enemies in an age where all ships were made of flammable wood and crew were constantly exposed on the upper decks.
Byzantine Dromons are a type of Galley unit which enjoys enhanced offensive capabilities.