For Roman coins and many modern coins the obverse is normally the side of the coin depicting the ruler's portrait. Hence the obverse of is also often referred to as "heads." For ancient coins, however, heads and obverse are not always synonymous. For all ancient coins, the obverse side of the coin is the side formed by the die set in the anvil used for striking. The reverse side of the coin is the side formed by the die struck by the hammer.