What happened to the Roman Empire at the time of the Middle Ages?

During the Middle ages, many "barbaric" nations have constantly attacked the Roman Empire, they spit into the West Roman Empire and the more wealthy Byzantines aka the East Romans. The West Roman Empire began to dissolve smaller because their army couldn't handle the constant attacks on them so they finally disappeared in 476 B. C. The Byzantines began to stretch even more until 1453 A. D. Just then After the fall of the Byzantines, a new Order of Romans came about called, The Holy Roman Empire sprouted up in Central Europe and they lasted until 1805 A. D. (I know this is more than the Middle Ages)