The fall of Roman Britain was driven by a fatal internal contradiction where the more power was sent to secure the land, the more likely that land was to be abandoned. This tension between local security and imperial ambition created a "British mistake" that repeatedly left the province defenseless against external raids and internal anarchy.

This paradox describes a cycle of military overreach where commanders used their massive frontier forces—totaling one-eighth of the empire's total army—as instruments to seize power in Rome. Each time these defenses were withdrawn, the "works of giants" began to crumble, leading to a rapid technological regression that forced the population back into a localized existence.

• Securing the frontier required a military force so large that its leaders became inherent threats to central authority. ...