Late roman officer and Lorica Musculata!

[Theodosius the Great]

On the majority of mosaic panels in S.Maria Maggiore in Rome, the soldiers wear armour broadly cut like a Hellenistic T&Y cuirass depicted in light blue with a red breast field. Some also clearly wear scale armour and some may wear mail. True muscle cuirasses are also shown but only worn by commanders. They are shown in light blue (iron/silver).

Also, I believe this panel shows a bronze musculata worn by the Archangel (upper right):
S.Maria Maggiore

~Theo