The rest, one might suppose, was left to the artist’s imagination. But it was not. Having been given his subject matter and his theme, he was bound further by strict conventions as to how sacred subjects were to be depicted. Jesus on the Cross had to be shown with his mother on the right and St. John on the left. The centurion pierced his left side. His nimbus contained a cross, as the mark of divinity, whereas the saints had the nimbus without a cross. Only God, the angels, Jesus Christ, and the Apostles could be represented with bare feet; it was heretical to depict the Virgin or the Saints with bare feet. The purpose of these conventions was to help the spectator identify the figures in the picture. Thus St. Peter was given a short beard and a tonsure; St. Paul was bald and had a long beard. It is possible that these conventions, which were immensely intricate, were actually codified in manuals which were passed on from master to apprentice in the workshops. As a general rule the ecclesiastics who drew up specifications did not invent the themes. Thus the learned priest who drafted the contract for the tapestry of St. Cecilia drew his material from the encyclopedia of Vincent de Beauvais. This was a compendium of universal knowledge covering the whole of history from Creation to the Last Judgment. It was a source book to which any man could turn in order to find the truth he happened to need. It contained all of human knowledge and the answer to all human problems. By the Thirteenth Century there were a number of these encyclopedias, of which the greatest was [p100] the _Summa_ of St. Thomas Aquinas. From these books churchmen took the themes which they employed their artists to embellish. The artist himself had no concern as to what he would paint, nor even as to how he would paint it. That was given, and his energies could be employed without the travail of intellectual invention, upon the task of expressing a clear conception in well-established forms. It must not be supposed, of course, that either doctrines, lore, or symbolism were uniformly standardized and exactly enforced. In an age of faith, contradictions and discrepancies are not evident; they are merely variations on the same theme. Thus, while it may be true that enthusiastic mediævalists like M. Mâle have exaggerated the order and symmetry of the mediæval tradition, they are right, surely, on the main point, which is that the organic character of the popular religion provided a consensus of feeling about human destiny which, in conjunction with the resources of the popular lore, sustained and organized the imagination of mediæval artists. Because religious faith was simple and genuine, it could absorb and master almost anything. Thus the clergy ruled the artists with a relatively light hand, and they were not disturbed if, in illuminating the pages of a Book of Hours, the artist adorned the margins with a picture of Bacchus or the love of Pyramus and Thisbe.