The historical evidence yielded by the coins of Greece and Rome is abundant, concise, essentially practical, and easily assimilated. Comparison of this evidence with what is provided by other branches of historical research is out of place, and seldom profitable: it is enough to point out the fundamental difference between coin-evidence and that which is furnished, for example, by works of art or inscriptions. A people's artistic or literary achievement is mainly a free expression of individual tendencies: though Phrynichus offended an influential section of public opinion with his play on the Sack of Miletus, and though Pericles was able to yoke Pheidias to his imperialist policy, it is true to say that such achievement was generally the result of free minds working their will. Artistic evidence for history is therefore ‘unofficial’, or informal. It is, of course, all the better for that; yet it must lack the precision which we look for in inscriptions—let us say, in an Athenian list of tribute-payments, or in a municipal charter under the Roman Empire. Inscriptions, indeed, are very often the product of private enterprise—the wish to record family honours, to mourn the dead parent, wife, or child, or to bless the emperor of the day; but they include a large class in which the information given is official in its purpose, and therefore full and accurate.