Those late Roman soldiers on the bottom belong to the 4th century with the reforms of Constantine (306 - 337 AD) and about as far back as Diocletian (284 - 305 AD). Look up the military reforms of those emperors or type in "4th century Roman Army" on internet search. Feel free to ask me more questions if you have any.
Because I was referring to oval shields from the area of Constantinople. I was searching for info if they existed during the 9th-10th century in the Byzantine Empire - if so what shapes and ornaments did they have.
I see.Maybe I can find some info for you because I am also very much interrested in it.Only Oval shields of those times used even much later were alredy used in the Roman army since late 2nd century so long before Constantine and long before medieval part of Roman history.