In 406, a confederate force of barbarians crossed the Rhine, breeching Roman imperial defenses on a vast scale, laying waste to Gaul and finally Spain, a rich province which had been at peace for over 400 years (and birthplace of the last emperor of a united Roman Emperor, Theodosius).
, father-in-law of the western emperor Honorius
and Commander of the western army (Magister Militum
), failed to effectively respond to the disaster, focusing his attentions on his long ambition of securing a hold over the eastern emperor, Arcadius, brother to Honorius and the wealth of the prosperous East. After three years of ever-increasing destruction of the West's imperial infrastructure, Honorius was persuaded to the arrest and execution of Stilicho, who despite his failure to stem the tide, had been an effective and skillful general of the legions.... Stilicho's execution prompted a mass "walk-out" by what was left of the Roman army in Italy, now heavily barbarized, and left Honorius without any effective force to stand off the attack of Alaric the Goth leader on Rome itself, in 410.
Honorius, for his part, has often been depicted as weak, foolish, even perhaps, mentally retarded... concerned only for the care of his chickens at his secure capital in Ravenna. Yet after Alaric's evacuation of Rome, with the help of several able commanders -- primarily his general and brother-in-law, Constantine -- he managed a rather effective political/military comeback for the empire. Though Britain and parts of Gaul and Spain were lost, the western empire had regained some of its position by his death, and his efforts may actually have staved off collapse for another 50 years.
In considering causes of the western empire's fall, it must be taken into account that the West's defenses did, in fact, suffer a dramatic collapse after a period of relative security under the able emperor Valentian and his sadly, less able descendants. While other factors certainly had bearing on the withering of western defenses, the purely military side of the collapse deserves to be properly considered.
In addition, since it was, in fact, Stilicho who had handled matters military in the West up to and beyond the 406 collapse, it may be that his failure to confront the growing weaknesses in imperial defense may entitle him to a larger share of blame than Honorius, who has often been singled out for special condemnation. And that Honorius' efforts to hold his empire together were of greater effect than has been given credit.