The name of coins is given to pieces of metal, on which the public authority has impressed different marks to indicate their weight and value, to make them a convenient medium of exchange.  By the word medals, when used in reference to modern times, is understood pieces of metal similar to coins but not intended as a medium of exchange, but struck and distributed to commemorate some important event, or in memory of some distinguished personage.  The name of medals, however, is also given to all pieces of money which have remained from ancient times.  The term medallion is given to medals of a very large size, many of them being several inches in diameter.  The parts of a coin or medal are the two sides; first, the obverse side, face or head, which contains the portrait of the person at whose command or in whose honor it was struck, or other figures relating to him:  this portrait consists either of the head alone, or the bust, half length, or full figure; second, the reverse contains mythological, allegorical, or historical figures.  The words around the border form the legend, and those in the middle the inscription.  The lower part of the coin, which is separated by a line from the figures or the inscription, is the basis or exergue, and contains subsidiary matter, as the date, the place where the piece was struck, etc.

Numismatics has the same divisions as history.—­Ancient Numismatics extends to the extinction of the empire of the West; the Numismatics of the middle ages commences with Charlemagne; and modern Numismatics with the revival of learning.

Medals indicate the names of provinces and cities, determine their position, and present pictures of many celebrated places.  They fix the period of events, frequently determine their character, and enable us to trace the series of kings.  They also enable us to learn the different metallurgical processes, the different alloys, the modes of gilding and plating practiced by the ancients, the metals which they used, their weight and measures, their different modes of reckoning, the names and titles of the various kings and magistrates, and also their portraits, their different divinities, with their attributes and titles, the utensils and ceremonies of their worship, the costume of their priests—­in fine, everything which relates to their usages, civil, military, and religious.  Medals also acquaint us with the history of art.  They contain representations of several celebrated works of antiquity which have been lost, the value of which may be estimated from the ancient medals of those still existing, as the Farnese Hercules, Niobe and her Children, the Venus of Gnidos, etc.  Like gems and statues, they enable us to trace the epochs of different styles of art, to ascertain its progress among the most civilized nations, and its condition among the rude.