Roman Legionary T-shirt portrays the Eagle standard (aquila) that was used as a symbol by the Roman legions. A legionary known as an aquilifer, the “eagle-bearer”, carried this standard. Each legion carried one aquila. Under the eagle standard there is a square plate with letters SPQR written on it. SPQR is an abbreviation for Senatus Populusque Romanus (‘The Senate and People of Rome’).
The aquila had semi-religious importance to the Roman soldier, it was not just a symbol of his legion. To lose a standard was extremely grave, and the Roman legions went to great lengths both to protect a standard and to recover it if it were lost