But the internal evidence of the vases is of even greater value, not only for the political, but still more for the social history of Greece. By the application of painting to vases the Greeks made them something more than mere articles of commercial value or daily use. Besides the light they throw on the Greek schools of painting, they have become an inexhaustible source for illustrating the manners, customs, and literature of Greece. A Greek vase-painting—to quote M. Pottier— is not only a work of art, but also an historical document. Even when all artistic qualities are lacking, and the vase at first sight is liable to be regarded as a worthless and uninteresting production, a closer inspection will often reveal some small point which throws light on a question of mythology, or of costume or armour. Or, again, an inscription painted or even scratched on a vase may be of surpassing philological or palaeographical importance. For instance, the earliest inscription known in the Attic alphabet is a _graffito_ on a vase of the seventh century B.C. (see Chapter XVII.), which of itself would command no consideration; but this inscription is valuable not only as evidence for early forms of lettering, but from its subject-matter. It is true that it need not necessarily be contemporary with the vase itself, as it may have been scratched in after it was made, but this cannot detract from its importance or affect its chronological value. Or, again, a fragment of a painted vase found at Athens bears the name of Xanthippos rudely scratched upon it; on the foot of another is that of Megakles (see below, p. 103). Both of these are undoubted instances of ὄστρακα, which were used for the banishment of these historical personages. They therefore provide a striking illustration of the institution of Ostracism, and bear out what we have said as to the importance of archaeological discoveries for the study of History. Historical or quasi-historical subjects are sometimes actually depicted on the vases, but this question must be reserved for fuller treatment in Part III., which deals with the subjects on vases in detail. In that section of the work we shall also deal with the relations of vase-paintings to ancient literature; and in the list of subjects taken from daily life (Chapter XV.) it will be seen what ample information is afforded on such points as the vocations and pastimes of men, the life of women, war and athletics, sport and education.