The reasons why the Western Roman Empire fell are still being debated today.  These excerpts discuss the combination of social, technological, and environmental factors that caused the destruction of the Western Roman Empire.

Vitruvius, Lead Pipes and Lead Poisoning:

Did the Romans poison their drinking supply by using lead pipes?

• Lead pipes were the standard material for water lines between the nearest castellum and the private house or street fountain, and in the main aqueducts.
• The ancient world seemed to have a glut supply of lead
• “Lead is indeed soluble in water but if the water has been flowing over sedimentary rocks (such as limestone), and not igneous rocks (such as granite), then it acquires a calcium carbonate which not only makes the water hard but also then separates out to form a shell of incrustation inside the pipes and water channels, effectively insulating them from water flowing inside.” (485)
• “This incrustation in Roman aqueducts certainly invalidates much of what has been argued about lead poisoning.” (485) 
• “In general Roman water was drawn from sedimentary catchments areas, formed an insulating deposit in the pipes, and was wholly safe to drink.” (488)
• However, if the water was sitting in the lead pipes for an extended period then the lead could seep through the incrustation (in taps)
• Since the Roman aqueduct system was designed on the principal of constant flow, lead poisoning could not have occurred
• Incrustation along with constant water flow through the lead pipes prevented lead from contaminating the water.

Baynes Article: The Decline of the Roman Empire in Western Europe:

• He refutes the environmental causes, like climactic change and soil erosion because the Eastern parts of the Empire experienced those same effects and did not collapse.
• The inability of the Emperor’s to protect the Western territories lead to the destruction of culture.  Barbarian invasions in these territories withdrew Roman soil and the revenues derived therefrom.
• Without money the Empire was unable to keep a mercenary army in the field and a fleet in commission.
• “In a word it was the pitiful poverty of Western Europe which crippled her in her effort to maintain that civil and military system which was the presupposition for the continued life of the ancient civilization.” (85)

Boak Article: Manpower Shortage and the Fall of Rome:

• A shortage of manpower had developed within the Roman Empire as early as the last quarter of the second century. (23) This shortage was caused by a retrogression of the inhabitants of rural areas.
• The shortage of manpower lead to the inability Marcus Aurelius to find the needed recruits for his army and he had to depend on the importation of barbarians to make up the deficit.
• In the Roman Empire, the major source of wealth was agriculture.  With the decline of manpower and an increase in taxes, production decreased and impoverishment increased.
• War, starvation, and disease lead to a decrease in birth rate in the mid third century.  The population trend was steadily downwards until the end of the West Roman Empire. (25)
• Decreas in Populationà Decrease in Manpowerà Decrease in Agricultural and Industrial Productionà Impoverishmentà Weak army and Barbarian recruits
• “The inability of the Roman government to prevent the settlement of these allies as well as other invaders within the Empire, coupled with the passing of the command of the army of the West into the hands of barbarian king makers was the immediate cause of the disintegration of the Western Empire.” (26)
• Lack of Military spirit also caused the emperors to depend on barbarians: self mutilation was often used to avoid military service, and desertions were quite frequnt.
• People also refused military service because they had no faith in the government and pride in protecting the Roman Empire
• “Decrease in agricultural products must be attributed largely to the shortage of rural labor and a failure to develop improved methods of cultivation and improved farm machinery which might have compensated for the decrease in manpower.” (28)
• Burdensome taxes made it impossible for the population to increase because families could not provide for a large family.
• “With declining manpower and increasing impoverishment, the Roman Empire in the West, unable to defend itself against disintegration from within and invasion from without, staggered slowly on to its inevitable dissolution.” (31)

Jones Book: The Decline of the Ancient World:

• The Western provinces were much more exposed to Barbarian attack than the Eastern provinces.
• “If the Western emperor failed to hold any part of the Rhine and Danube fronts, he had no second line of defense; the invaders could penetrate straight into Italy and Gaul, and even into Spain.” (362)
• The peasants in the West were very poor because of the heavy burdens of taxation.
• The aristocracy in the West controlled the administration, and made sure that the peasants had the burden of taxation, while they were granted immunity.
• “The heavy economic burden imposed by the increased size of the army overstrained the recourses of the empire and produced a number of weaknesses. (365)
• Since the farming and transportation technology was very primitive, it took a lot of manpower to grow crops and clothe and feed the soldiers.  And since the East was no longer looking out for the West, it was hard to raise funds.
• Because the population of peasants was decreasing, this lack of manpower lead to a lack of wealth and food.
• Increase of the aristocracy, in shapes of senators and priests added to the burden of taxation on the peasantry.
• Nobles and peasants both were inert and had no pride in protecting the walls against attack.  The wealthy nobles sometimes allied with the barbarians and the peasants often fled during an attack.  Christianity helped to encourage apathy and lack of public spirit because of the teachings that “salvation was only to be found in the world to come.” (369)
• The increasing pressure of the barbarians concentrated on the weaker half of the empire, along with a lack of pride to defend it, that lead to the collapse.

Chastel Book: The Sack of Rome:

• More modern example to show how important a role luck can play in a military siege.
• When the imperials invaded Rome an intense fog prevented the cannons from protecting the city.