The silver denarius, patterned after the Greek drachma, was introduced about 212 BC. Soon after, the prior copper coin (aes, or libra) began to be debased until, by the onset of the empire, its weight had been reduced from 1 pound (12 Roman ounces) to half an ounce. By contrast the silver denarius and the gold aureus (introduced about 87 BC) suffered only minor debasement until the time of Nero (AD 54), when almost continuous tampering with the coinage began. The metal content of the gold and silver coins was reduced, while the proportion of alloy was increased to three-fourths or more of its weight.