Roman Coin Denominations:
Relative Sizes and Values
Coins of Imperial Rome from Augustus to Caracalla
Source: David Van Meter (2000). The Handbook of Roman Imperial Coins. Laurion Press.
Photos of Quadrans and Aureus courtesy of Michael Moriarity at topcoins.com. Photo of Quinarius courtesy of Classical Numismatic Group.
For complete table of Roman coins and their contemporary values check out this site
For an essay on the evolution [or deevolution] of Roman denominations, go to Doug Smith's site.