Per Gorchestopher's comment, the above image is a deviantart (e.g. fanmade) picture by Stephen Howard showing a "Celtic Supergirl", part of a series of 73 "out of time" images suggested by fans.
On the subject of ancient Rome, there have been some time-travel stories you may be interested in including "Lois Lane, Slave Girl!" (from Superman's Girlfriend Vol 1, #33)
and "Challenge of the Superfriends" in which Superman, Batman and Robin are transported to Ancient Rome to face lions (well, lion) in Caesar's gladiatorial arena.
