The Roman Empire reached its greatest size under the reign of Trajan in 117 AD. To aid in administration, it was divided into provinces. The number of provinces changed over time as territories were gained or lost, and as larger provinces were divided into smaller ones. There were 46 provinces under Trajan, a figure that would grow to 96 by the reign of Diocletian (285-305).
This map depicts the deployment of Rome's legions when Rome's first emperor, Augustus, died in 14 AD. Augustus and his successors distributed the Roman army along the frontier, ensuring that no single general had command of more than a small fraction of Rome's troops at any one time. And emperors reduced the soldiers' dependence on their commanders by paying them salaries from the imperial treasury.
At its peak, the Roman Empire held up to 130 million people over a span of million square miles. How could such a powerful empire collapse? Simple, the real effects of debasement took time to materialize... and then exploded.