Historian Mary Beard closes her four-part series with the biggest question of all: why did Rome fall? She walks the fortifications built across Britain and Germany, reading them as evidence of an empire increasingly occupied with holding its own borders rather than expanding them. Rather than accepting the old story of barbarian hordes overwhelming a passive empire, she reexamines what the 'Barbarian Invasions' actually looked like on the ground and argues the pressures from outside were matched by convulsions from within. Unconventional emperors defy the expectations of the Roman elite, and the state's traditional religious order collides with the uncompromising beliefs of Jews and Christians. Beard weighs whether Rome was destroyed or simply transformed, tracing its afterlife in the institutions, infrastructure, and imperial symbolism that later empires borrowed wholesale. Location filming across former frontier territory grounds the argument, and Beard's own skepticism toward tidy collapse narratives gives the episode its edge.