Byzantium: How an Empire Lasted a Thousand Years After Rome

About eleven hundred years, on the most commonly used framing. Dumbarton Oaks, which has run a Byzantine studies programme continuously since 1940, defines the civilisation it studies as the Byzantine Empire "from the fourth to the fifteenth century". The end point is precise: the Byzantine and Christian Museum in Athens records that Constantinople fell to Sultan Mehmed II on 29 May 1453 after a two-month siege.

The start point is not precise at all, and that is the more interesting half of the question.

Why "how long" has no single answer

Every candidate start date encodes an argument about what the Byzantine Empire was.

If it began when Constantine refounded the city, the empire starts in the fourth century and Dumbarton Oaks's bracket applies directly. If it began when the Roman Empire was administratively divided, you get a slightly later date and a claim that the east became a separate thing. If it began when the western imperial line ended in the fifth century, you are implicitly saying the eastern empire only became "Byzantine" once it was alone — which is a strange thing to say about a state that had not changed.

And if, as many specialists in late antiquity argue, there is no sharp transition at all, then the question has no answer because the object it asks about was never created on a particular day.

This is not evasion. It is the same structural problem set out in why Rome fell, and it is worth reading that argument rather than having it repeated here: the date you pick follows from the definition you adopt, not the other way round.

The empire did not call itself Byzantine

The label is modern scholarly shorthand, and it comes from the city's older name. UNESCO's inscription for the Historic Areas of Istanbul describes the Historic Peninsula as the ground "on which the former Byzantium and Constantinople developed" — Byzantium first, Constantinople after.

What the same UNESCO text calls the state itself is more accurate: Istanbul was "successively the capital of the Eastern Roman Empire, and the Ottoman Empire". Eastern Roman is the description that would have made sense to the people living under it. They were running the Roman state, from a Roman capital, under Roman law, and the fact that they spoke Greek does not change that any more than the Latin-speaking western provinces of an earlier century made Rome Italian.

Using "Byzantine" is fine — it is universal in the literature and nothing is gained by refusing it. Knowing that it is a later convenience is what stops you from treating the eastern empire as a successor state rather than a continuation.

The city that made the duration possible

A great deal of Byzantine longevity is a matter of geography and engineering.

UNESCO records that the Historic Peninsula was surrounded by ancient walls built initially by Theodosius in the early fifth century, and that the wall of Theodosius II, with its second line of defence created in 447, was one of the leading references for military architecture. Water on three sides — the Golden Horn to the north, the Bosphorus to the east, the Sea of Marmara to the south — and a double land wall across the fourth made Constantinople an extraordinarily difficult target for a thousand years.

Inside, the city produced work that set standards elsewhere. Hagia Sophia, whose vast dome UNESCO credits to sixth-century architectural and decorative expertise, "became a model for an entire family of churches and later mosques", and the mosaics of the palaces and churches of Constantinople influenced both Eastern and Western art.

The city's later layers are Ottoman and equally significant: the fifteenth-century Fatih complex and Topkapı Palace, extended into the nineteenth century; the Süleymaniye and Şehzade mosque complexes by the chief architect Sinan, which UNESCO calls the climax of sixteenth-century Ottoman architecture; the seventeenth-century Blue Mosque; and the New Mosque near the port, completed in 1664. One skyline holds both empires, which is precisely why UNESCO inscribed it.

Ravenna: Byzantium in Italy

The eastern empire was not confined to the east, and the clearest surviving evidence of that is in north-eastern Italy.

Ravenna became the capital of the Western Roman Empire in 402 CE and remained prominent as first an Ostrogothic and then a Byzantine capital in Italy through the fifth and sixth centuries. Its eight inscribed monuments — the Mausoleum of Galla Placidia, the Neonian Baptistery, the Basilica of Sant'Apollinare Nuovo, the Arian Baptistery, the Archiepiscopal Chapel, the Mausoleum of Theodoric, the Church of San Vitale and the Basilica of Sant'Apollinare in Classe — were built between the fifth and sixth centuries and decorated with marble, stucco and mosaic.

Those buildings are the physical residue of the sixth-century campaigns that returned parts of Italy to imperial control. They are also a useful corrective: for a period, the Roman Empire genuinely did rule Italy from Constantinople.