Disclaimer thingy: I am writing about this because of something I learned during our last class, something relevant to today's political and cultural maps. If you want an actual history lesson with dates and stuff, try Wikipedia.
The rise and fall of the Roman empire did not happen with any single event. The fall was actually a combination of reorganization, erosion and invasion that took about a millenium to complete and yet the Roman empire lives on, its spirit divided into three.
Sometime in the 5th century CE, emperor Constantine, who simply didn't like the city of Rome, set up shop in Byzantion, and renamed it Constantinople. The empire then basically split into a western and an eastern part. Rome was already being abandoned by its population for various reasons, so when someone asked, "Shouldn't we elect an emperor of Rome?" the answer was basically a shrug. The Roman Empire, as a military power, continued in the east, while the Goths finally seized Rome in the west.
In the west (west of Greece), the population had been going through a shift in organization and attitudes. For one, the increase in Christianity led to the freeing of the slaves, and a movement away from a purely urban lifestyle. Christianity was actually an urban religion, so this development was new for the Christians, too. In lieu of political leadership, the church stepped in as the unifying factor. In fact, as the empire crumbled in the west and local peoples took back self-rule, there was still a continuity and stability thanks to the church and its use of Latin. For centuries, anyone in Europe had access to all the knowledge ever written in the empire, simply by learning Latin. This plus its status with the common people, made the church an umbrella organization even trumping all the kings of Europe. The Roman Catholic church even today has rituals that come directly from Roman Empire military ceremonies.
In the east, the Roman Empire with its succession of emperors and local senate, abandoned Latin and opted for Greek. In this area, basically today's eastern Europe, the church had a different status with the pope being second in command to the emperor. Eventually, this evolved into today's Orthodox church and the east-west divide also came to influence the choice of alphabet.
To this day, the divide between the eastern and western administrative divide of the Roman Empire can still be clearly seen: Just make a note of which countries are or were Roman Catholic (like Poland). These countries seek west and after the fall of the Sovjet Union (which thought it could be a new Roman Empire) and the Warsaw pact, they have made a point of joining the European Union. Our laws, our system of justice, and even many main highway routes, are also from Roman times.
So we know where the intellectual and political aspects of the empire went (west and east, respectively). What about the third aspect, the empire idea, where did that end up? With the Moslems, that's where. They also kept the urban focus of the Romans, but not their language or administration.
I shall now return to my novel. Speaking of which, The Happiness Project has some writing advice.