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".
The Roman army standards - The signa militaria, or military standards served as landmarks between different Roman units, serving as a rally point in the chaos of battle. The various units that made up the Roman army needed some kind of recognizable symbol to be followed in the confusion of combat. So it was very important that the naked eye could see and know, what it was for.