The Venetians used to say that whenever the Golden Horses were moved, an empire fell

There they are now, out of the sun at last. Through the door of their last resting-place you may see their forms, proud as ever, silhouetted against the half-light from the windows. Their hoofs are raised, as always, in a noble gesture of greeting, companionship or compassion. Their heads are turned still, fraternally towards each other. But the life has gone out of them at last, as the power and purpose have left Venice. The Venetians used to say that whenever the Golden Horses were moved, an empire fell – the Byzantine Empire in 1204, the Venetian Empire in 1797, the Napoleonic Empire in 1815, the Kaiser’s Empire in 1918,Hitler’s Empire in 1945. This their last move, though, is no more than an obituary gesture, a long farewell, a recognition that the glory of Venice has gone, and only the forms remain.

J. Morris, The Venetian Empire (1980), 187

To Europe Byzantium is a symbol of its honour

The realm of the last Roman Emperor is only the size of a plate, merely a gigantic circular wall surrounding churches, the palace and a tangle of houses, all of them known as Byzantium. Pitilessly plundered by the crusaders, depopulated by the plague, exhausted by constantly defending itself from nomadic people, torn by national and religious quarrels, the city cannot summon up men or courage to resist, of its own accord, an enemy that has been holding it clasped in its tentacles for so long. The purple of the last emperor of Byzantium, Constantine Dragases, is a cloak made of wind, his crown a toy of fate. But for the very reason that it is already surrounded by the Turks, and is sacrosanct to all the lands of the western world because they have jointly shared its culture, to Europe Byzantium is a symbol of its honour.

S. Zweig,'The conquest of Byzantium' (1940), tr. A.Bell, in Triumph and Disaster: Five historical miniatures (2016), 69-70

One can and may blame the wicked Fourth Crusade

Though one may bitterly deplore, as I do most fervently, that the Turks ever set foot in Europe, it would be absurd to blame them for the destruction of the Byzantine Empire as it would be to arraign the laws of hydrostatics for damage by flood. But one can and may blame the wicked Fourth Crusade for making that destruction inevitable and bringing about the wreck of eastern Europe for centuries

P.L. Fermor, Mani (1958), 295