Constantinople wasn't part of the muslim world in the middle ages, it was the center of eastern orthodox christianity, it lost its fight with the western branch

Constantinople wasn't part of the muslim world in the middle ages, it was the center of eastern orthodox christianity, it lost its fight with the western branch, and eventually was conquered by the muslims :) (well, depends on your definition of middle ages, but the opinion that middle ages ended with the fall of Constantinople is quite popular).