One of the main problems that resulted from the large size of the Roman Empire was that of ensuring that political control reached every corner of the empire. While the area surrounding the cities of Rome and Constantinople were easily controlled, more remote areas of the Empire became harder to account for. This problem grew as the "barbarian" groups that surrounded the Empire became stronger.
The fact that the government was set up to rule a small city meant that it was not able to oversee remote areas effectively. In turn, this allowed such areas to develop alternative structures of power. This was enhanced by the fact that there was no clear heir when the emperor died. Because of this, people did not feel a strong attachment to the government, and instead felt closer to their local leaders. This allowed people to take advantage of the situation by becoming leaders in their communities. Such leaders enjoyed an amount of privilege and respect that was incompatible with the Roman system. Such fragmentation of political power set the foundations for the development of feudalism and the relationships between lords and vassals after the fall of the Roman Empire.