Two of the many explanations for the Fall of Rome are the splitting up of the Roman Empire and the presence of lead in the drinking water leached in from the water pipes or leached from cooking and pottery.

See Lead Poisoning. For problems on the theory and evidence for lead poisoning, read: "Old Wine in Old Lead Bottles: Nriagu on the Fall of Rome," by Charles Robert Phillips III. The Classical World, Vol.

78, No. 1 (Sep. - Oct., 1984), pp. 29-33.

"Does anyone know why the Roman Empire (after Rome falls in 476 A.D.) is called the Byzantine Empire? I have read that around the 300s A.D. the capital of the western empire was moved into northern Italy. Is the Byzantine Empire just a modern name that was given to the empire after the west collasped?" - from ZULULAND1: Read the Ancient/Classical History Forum thread for answers.

Division of the Empire

Rome The Late Empire [URL = www.wsu.edu/~dee/ROME/LATE.HTM]
Richard Hooker marks the Fall during the reign of Diocletian (284-305) when the Empire was split into two halves. Each half had a senior augustus and a junior caesar. Together these four rulers were known as the "tetrarchy." While the tetrarchy didn't last long, the division of the Empire became the norm.

Fall of Rome
Adrian Dorrington says the Empire was split not just geographically, but culturally, with a Latin Empire and a Greek one, the latter of which survived because it had most of the population, a better military, more money, and better rulers.

Lead

Lead and the Fall
A bibliography of sources since the nineteenth century that have suggested lead poisoning led to the Fall of Rome.

Rome and Roman Empire Maps

Frontiers of the Roman Empire
Source: [URL formerly at ccat.sas.upenn.edu/bmcr/1994/94.09.01.html] CR Whittaker's Frontiers of the Roman Empire.
The extensive empire put such a strain on Roman coffers Emperor Honorius sent letters to the Roman cities in England to tell them they'd have to fend for themselves. [This marks the end of the period of Roman Britain.]

By the third century, it was sometimes hard to tell Roman from barbarian. In addition, Romans regularly employed "barbarians," -- the Huns and Vandals -- sometimes in double crosses:
The Roman general Aetius used Huns in battle in Germany and Gaul, but then in 451 he used the Burgundians and Visigoths of this region to fight against Huns (led by Attila).
In a factional struggle with the leadership in Ravenna, the Roman comes africae invited the Vandal King Geiseric to Africa.

References:

• _{Did Rome Really Fall?}
• _{[URL formerly http://www.etss.edu/hts/hts2/notes11.htm]The End of the Western Empire}

Rome and Roman Empire Maps | Rome Era-by-Era Timeline

The 4 Parts of This Fall of Rome Article:

Why Did Rome Fall? | Decay, Christianity, Vandals | Economy | Lead and the Split

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