The settlement of Ravenna may date from the Villanovan period of Italy, the earliest Iron Age culture of central and northern Italy. The fact that Ravenna began as a settlement on a lagoon, like Venice, may indicate even earlier habitation than the Villanovan era.

Many European prehistoric settlements were groups of houses built on stilts in the middle of lagoons for purposes of defense against marauding tribes. Such lagoon or lake settlements date from the Bronze Age, some 4,500 years ago.

Simon Adams writes, in Castles and Forts, "most of these villages were built on the shores of lakes or by rivers—often located on small islands that could easily be fortified. A group of around 20 rectangular houses stood on stilts to cope with seasonal flooding".

Not much attention was paid to Ravenna, as the city did not threaten Rome, and the legions were needed to consolidate Roman power in Italy and elsewhere. In the first century b.c.e. Rome became involved in the civil wars that would end with the fall of the Republic to Julius Caesar.

Ravenna became accepted as part of the Republic in 89 b.c.e., and in 49 b.c.e. gained historical importance as the city from which Caesar marched to "cross the Rubicon" in the drive for power that would ultimately make him dictator for life. He did not live long to enjoy it —in March 45 b.c.e. he was killed in the Roman Senate, at the foot of the statue of his great rival, Pompey.

Caesar’s great-nephew Octavian, who would rule as Emperor Augustus Caesar (27 b.c.e.–14 c.e.), realized the importance of Ravenna to Roman control of the Adriatic Sea. He established a military harbor for the Roman fleet at nearby Classe, in part to patrol against pirates. Pirates in the second and first centuries b.c.e. had become a major threat to Roman commerce in the Adriatic and the eastern Mediterranean Seas.

With the onset of confl ict with Persia in the East, Ravenna became the Roman gateway to Asia. Emperor Trajan (98–117 c.e.) built an aqueduct to ensure a supply of freshwater for this strategic city. During the fourth century c.e., the Roman Empire came constantly under the assault of barbarian tribes.

The imperial capital was moved from Rome to Milan and finally to Ravenna by Emperor Honorius—the ruler of the western half of the empire—in 402 c.e. Honorius did so because it was easily defended from its location on the lagoon.

In 409 Honorius’s wisdom soon proved correct. When Alaric, king of the Visigoths, marched to sack Rome, he by passed Ravenna. In 476 the German warlord Odovacar of the Heruli tribe finally brought an end to the Roman Empire in the West by deposing the emperor Romulus Augustulus.

The Eastern Roman emperor, Zeno, recognized the rule of Odovacar but later sent Theodoric to reconquer Italy for the empire. After the death of Odovacar in 493 Thedoric effectively carved out his own kingdom, with Ravenna at its center.

Eastern Roman emperor Justinian I, aided greatly by his consort, Theodosia, aimed at nothing less than the total reconquest of Italy for the empire. His invasion began in 535, and he largely achieved his goal.

Ravenna became the center of the restored Roman Empire in northern Italy in 539. The area was considered of prime military importance because it provided the Eastern empire not only with a strategic center in Italy but also with a major base on the Adriatic for the navy.

And, as in the days of Trajan, the Danube remained of great importance as a frontier against the barbarians. For this strategic reason Ravenna became the administrative focus for an imperial exarchate, or military colony, in much of northern Italy.

The exarchate was formed under Emperor Maurice (582–602), largely to combat the incursions of the Lombards, who had invaded Italy in 568 from what is today’s Austria. The military force commanded by the exarch at Ravenna became known as the Exercitus Ravennae and came to include many Italians, in addition to soldiers from the Byzantine army.

However, during a period of fighting the Lombards, the Muslim conquest erupted from what is now Saudi Arabia. Inspired by the teachings of the prophet Muhammad, the Muslims overran the Holy Land. Between 674 and 678 the Muslims even besieged Byzantium, before finally being driven away.

The result in Italy was a drastic loss of Byzantine power. In 726 the citizens of Ravenna defeated an expeditionary force sent by Emperor Leo III to reimpose strong Byzantine rule. The area was gradually diminished under almost constant pressure from the Lombards.

In about 750 the Lombards finally conquered Ravenna. The Byzantines, faced with Persian and barbarian invasions, could not keep their hold on Italy, even when supported by their powerful navy, whose oared warships, or dromonds, were the most powerful battle ships of their day.