The Two Roman Capitals

It is striking to see the differences between the ruins of ancient Rome and ancient Constantinople (now Istanbul). When the Roman Empire fell in the West in 476 CE, it continued in the East until 1453 CE. Western historians use a historiography (how a history is told) that the Roman Empire fell in 476 CE and label the continuing Roman civilization in the eastern Mediterranean as "Byzantine" as if it was a new empire.  It wasn't, but the continuing Roman Empire centered on Constantinople did continue to develop and evolve through the Middle Ages into something different than ancient, classical Roman civilization.  And it was a Christian Roman world affiliated with Eastern Orthodoxy.  

To those living in the former western Roman provinces and even Rome itself, Rome as they knew it had fallen. The Dark Ages had come, and the ruling Church was Roman Catholic. Western European history continues this perspective until this day. It's the historiography America inherited. 

Ironically, it was probably these Christian 'barbarians' from the former Western Roman Empire that mortally wounded the final Roman world in the East. Western Catholic Crusaders led by Venice betrayed and sacked Christian, Eastern Orthodox, Greek-speaking Constantinople in 1204 during the 4th Crusade. Some estimate 2/3s of the world's wealth at that time was then in Constantinople. 

The Crusaders then installed a series of Latin Emperors until ousted by the locals.  The Crusaders did a huge amount of damage and looting to Constantinople.  The four bronze horses that now adorn St. Mark's Basilica in Venice were looted from Constantinople. (The originals are now in a Venetian museum.)  The last Latin emperor of Constantinople even stripped the Imperial Palace of its metal roof tiles and sold them. 

Crusaders also chopped off the head of a metal serpent statue in the Hippodrome. The coiled, headless relic remains in Constantinople to this day. 

The city never recovered, and when the Turks finally conquered the city in 1453, much of the old Imperial Palace and Roman city were in ruins.  Still, Istanbul remained a vibrant city with a large population that rebuilt and maintained important parts of the Roman city.  The Hagia Sophia is the most famous surviving building.

Rome, however, didn't fare as well. By the 1300s much of the city was abandoned. Local families fortified ancient buildings during the Dark Ages. The return of the popes from Avignon in France in the late 1300s set off a building boom with the papal powers basically using the old Roman buildings as a quarry for pillars, marble, statues, mortar, etc.  So the Roman Forum and other once huge structures in Rome are in fairly bad shape. The structures that remain mostly intact like the Pantheon often survived by being converted into churches.