More than a city or even an empire, Byzantium was a civilization, with deep roots in antiquity but bequeathing little to the future except for its cultural inheritance — the Renaissance and Orthodox Christianity.
This is sarcasm, yes?
Ah, but what about its accomplishments before its demise? From the 600s to the 1400s, it was a bulwark against a surging Islam. In N.Africa, the green flag swept all of the way to the Pyrenees and into France and in the east it took out the Persian Sasanian Empire which extended Islam rule to the Indus River. Yet to the North, Byzantium withstood multiple onslaughts for 700 years. In fact the Ottomans did not get into Europe until the last years of the 1300s.
This was more, far more than nothing!