Everytime I see a picture of a centurion, no matter where, or from what source be it history channel or re-enactments, the centurions don't have shields. They also had to be right there... I mean right there in the thick of it all to watch for acts of bravery, give orders, cover wounded, and hold the line.
IF you ever have the chance, watch the action packed documentary; Life and Death in Rome: The Legions
Fortunately I taped it, but I can not find it anywhere to purchase it. It is awesome. It follows a legionnaire, Maximus. Archeologists found his grave, and they use the decor on his grave to try to piece what his life was like in the army. There is some good stuff on centurions in there too, from training to battle.