In economics, a place where coins are made according to exact compositions, weights, and dimensions, usually specified by law. The first state mint was probably established by the Lydians in the 7th century bc. The art spread through the Aegean Islands into Italy and other Mediterranean countries, as well as to Persia and India. The Romans laid the foundations of modern minting standards. Coining originated independently in China in the 7th century bc and spread to Japan and Korea. In medieval Europe, mints proliferated as every feudal authority—kings, counts, bishops, and free cities—exercised the mint privilege; the wide variation in coinage that resulted often handicapped commerce. Most countries now operate only one mint, though the U.S. has two active mints, in Philadelphia and Denver. Proof sets of coins for coin collectors are minted in San Francisco. Countries not large or prosperous enough to establish a national mint have their coins struck in foreign mints. Many mints perform functions other than minting, notably refining precious metals and manufacturing medals and seals. See also currency, money.