The death knell of the Eastern Roman Empire was the Fourth Crusade in 1204, which attacked, looted and took over the city and carved up its territories.
The exiled Eastern Romans of the Nicean Empire reclaimed Constantinople from the Latin Empire, the so-called 'Empire of Romania' after about 60 years but the Eastern Roman Empire after that was more like a successor state.
Most of Constantinople was in ruins and uninhabited, like a ghost city and most of its monuments destroyed or looted.