Legion coinage

Legion coinage or Legion money is a type of currency in Fallout: New Vegas produced by Caesar's Legion.

Background
Caesar's Legion uses two types of coinage, the denarius and aureus, as their main form of currency. They are presumably named after the Roman coins of the same names. They are minted by the Legion from scavenged silver and gold, with each coin bearing the profile of Caesar. Despite Caesar's poor relations with the other factions in New Vegas, Legion currency is still accepted as payment in the Mojave Wasteland, even from NCR merchants, owing to the precious metals the denarius and aureus are minted from. The exchange rate is 4 bottle caps to 1 denarius, and 100 bottle caps to 1 aureus.

Legion denarius


 The denarius (silver), which bears an image of a younger Caesar on the obverse and Caesar, Joshua Graham and Bill Calhoun on the reverse. The inscriptions are in Latin, "Caesar Dictator" meaning "Dictator Caesar" or "Absolute Ruler Caesar" on the front and "Magnum Chasma" meaning "Great Abyss" or "Great Fissure" on the back, referring to the Grand Canyon. The symbolism is simple - the denarius commemorates young Caesar's journey to the Canyon and his first victories as a dictator of the Grand Canyon tribes. 
 * For the mangled version found in Fallout: New Vegas, see: Legion denarius, mangled.

Legion aureus


 The aureus (gold), which bears the portrait of the older Caesar on one side and the symbol of the 10th Legion (the bull) on the other. The inscriptions are in Latin, "Aeternit Imperi" meaning "For the eternity of the empire" on the front and "Pax Per Bellum" meaning "Peace through War" on the back. 

Legion double aureus
When post-endgame play for Fallout: New Vegas was being considered, J.E. Sawyer intended for the Legion to mint a commemorative double aureus featuring a depiction of a conquered General Lee Oliver on the front and a symbolism for the Courier. The idea for the coin is inspired by the minted by Julius Caesar after his victory over the Gauls.

Behind the scenes


Both the denarius and aureus were a form of Roman currency used during the time of the Roman Empire, with the aureus being valued at 25 silver denarii. 
 * Both of the above quotes come from J.E. Sawyer (source #1, source #2)