The Fall of the Roman Empire

Gibbon attributes the fall of the Roman empire largely to the introduction of Christian monasticism, when "the sacred indolence of the monks" sapped the vitality of Roman civilisation.

Gibbon was wrong!

One of the main causes of the Roman Empire's collapse was galloping inflation. While it was expanding, it was ok, but when it ceased to expand it faced major problems, from soon after the reign of Marcus Aurelius. Once the Romans stopped conquering new lands, the flow of gold into the Roman economy decreased, and the prices of goods increased. The maintenance of a standing army was an increasing burden on the Imperial treasury, and the failure of Emperors to address the problems of inflation led to a rise in depositions. In the period 186-286 AD, Rome had had 37 different emperors - 25 of whom were removed from office by assassination.

To maintain the army meant to reduce living standards back home, and so the defence budget was cut over time, meaning that borders were ill-defended against invasion.

Monks didn't come into it. If anything, at this stage, the monasteries became the few surviving centres of learning (if they survived) preserving texts (such as the codifications of Roman law and learning) as the rest of the Western Roman Empire collapsed under internal pressures and barbarian invasions.