This scenario will represent a broard spectrum of centuries to represent most of Rome's historical allies and enemies. There will be 22 main civilizations and many minor nations as well. Minor civilizations will have a leaderhead image. Each major civilization will have its own 2D leaderhead image so DX9 will be the recommended play setting, or otherwise if you wish to play DX10/DX11 then you will have to edit GraphicsSettingsDX11.ini (should be located somewhere like ...\Documents\My Games\Sid Meier's Civilization 5) with the following change UseScreenShots = 1
The Romans will be the only playable civilization, but here is a partial list of the civilizations and it's respective leader which you will encounter. There will be many more added to this list.
Again, this scenario covers a broad spectrum of centuries.
Carthaginians - Hannibal
Arverni - Vercingetorix
Huns - Attila
Macedonians - Philip V
Cimbri - Boiorix
Achaen League - Critolaus
Helvetii - Divico
Numidians - Jugurtha
Pontus - Pharnaces II
Cherusci - Arminius
Catuvellauni - Caratacus
Suebi - Ariovistus
Belgae - King Galba
Nervii - Boduognatus
Egyptians - Cleopatra
Armenians - King Tiridates
Parthians - Artabanus IV
Seleucids - Antiochus III
Iceni - Boudica
Dacians - Decebalus
Marcomanni - Ballomar
Thracians - Rhescuporis II
Quadi - Areogaesus
Alamanni - Chnodomarius
Visigoths - Alaric
Vandals - Geiseric
Ostrogoths - Totila
Franks - Butilinus
and more....