From the Germanic invasions of 406-409 onwards, the Church and its bishops developed a major role in the civic organization against external enemies; and this is especially true at a time in which the Roman army could not face the many Barbaric hordes who wandered along the imperial West. The ecclesiastical authorities protected their cities, not only by means of their moral appeals but also by assuming the military defense itself.
That was the case of Gregory the Great, bishop of Rome in a very difficult moment, menaced by different Lombard armies and abandoned by the scarce Byzantine troops, which were compelled to garrison Ravenna or Perugia instead of protecting the Vrbs. So, Gregory must manage to arrange the defense –supplying food for their fellow citizens, organizing the walls guard– and he even sets himself up as the main “strategist” of the imperial forces in the Roman Duchy as some letters of the Registrum prove. Aside from many quotations concerning civic defense, the epistle 2, 4 will be especially analysed in the light of new historical and archaeological evidences drawn from the recent studies by Zanini, Borri or Ravegnani.