The legions were not allowed into Rome itself, except during parades celebrating a great victory. Only the personal guards of the emperor, known as the Praetorian Guard, were allowed in the city limits.
Roman testudo (tortoise) formation. In Ancient Roman warfare, the testudo or tortoise formation was a formation used commonly by the Roman Legions during battles, particularly sieges. Testudo is the Latin word for "tortoise". The Greek term for this formation is "chelone" and during the Byzantine era, it seems to have evolved to what military manuals of the era call the "foulkon".