A small, flat piece of metal bearing a design commemorating a person or event and produced in multiple copies; usually it resembles an outsize coin, with a profile portrait on one side (the obverse) and a complementary image, generally alluding to the subject's character or achievements, on the other side (the reverse). Although there are precedents of a sort in ancient Roman art, medals as we know them originated in the 15th century, inspired by the Renaissance interest in antique coins (with their vivid portraits of emperors). The majority are circular (typically between 5 and 10 cm (2–4 in) in diameter), but a few are ovals or other shapes; most were made in honour of a particular individual, but some commemorate significant events (such as a battle or the foundation of a major building). Both sides usually have an inscription in Latin (or occasionally Greek). Like the later portrait miniatures, which they helped to inspire, medals were often worn round the neck. The father of the art form was Pisanello, who began making medals in about 1439–40. His innovations were soon imitated and during the second half of the 15th century the production of medals was established in virtually every notable art centre in Italy. In the 16th century the fashion spread to other countries, particularly Germany, where a specialist profession of medallist developed. Most early medals were made of bronze (lead and silver were sometimes used) and were produced by casting, like miniature works of sculpture. In the early 16th century, however, machinery was introduced by means of which the design could be stamped on a blank piece of metal. Improvements in technology led to mass production, with a consequent drop in artistic standards (and also a broadening of scope: the first military campaign medal, for example, was issued in 1650 to commemorate Oliver Cromwell's victory at the Battle of Dunbar). However, there have been periodic revivals of interest in producing cast medals in the original Renaissance fashion.