They form a curious link between the Pagan and Christian world of thought. According to Greek ideas, Sibyls were women under the inspiration of the Deity, but they are not spoken of at all by either Homer or Herodotus: and the first Greek writer who mentions them is Heraclitus (_circa_ 500 B.C.). Aristophanes, Plato and other early writers only mention _one_: Heraclides Ponticus, a pupil of Plato, speaks of _three_ (the Erythraean, Phrygian, and Hellespontine); but Pausanias gives _four_ (the Libyan, Erythraean, Cuman, and Hebrew). Of these the oldest was said to have been the Libyan: though the best known to modern times are undoubtedly the Delphic, the Cuman (visited by Æneas), and the Tiburtine, who is said to have foretold Christ to the Emperor Augustus. By Christian writers they are spoken of first in the second century A.D., but do not appear in art until the eleventh. In the handbook of Mount Athos we read of the “_Wise_ Sibyl”; and side by side with David, one of these prophetesses appears in the Sequence of Thomas of Celano: the Dies Irae (_circa_ 1253).[33] They have no place in early mosaics, but one of the most ancient representations of a Sibyl is that of the Tiburtine in the church of Sta. Maria Aracoeli in Rome. The first, and perhaps the most poetic Choir of them, is on the pulpit of S. Andrea at Pistoia, sculptured by Giovanni Pisano in 1301; but from that time, until the fifteenth century, we find no other _groups_ of them. Then appeared a great many representations, and their number increases rapidly to as many as thirteen, the last of whom is the Queen of Sheba, who is called Nichaula, and is fabled to have foretold to King Solomon the Advent of a Messiah. The usual numbers, however, are _three_, _four_, _six_ and _ten_; and in such groups they have been designed by the greatest artists. Giotto,[34] Perugino,[35] Pinturicchio,[36] Raphael,[37] and Michael Angelo,[38] are but a few of these. Not only throughout Italy, but to the Northern Art Schools of Germany and Flanders, the same cult spread; and we find them introduced into sculpture, painting and engraving. Sibyls assist, as interested and sympathizing spectators, in every scene of Holy Writ. They meet us even in painted windows and illustrated books of devotion.[39] It is therefore not remarkable to find them here; and, if one recognizes the attitude of mind, with which they were regarded by the Renaissance Catholic, they are even most appropriate. The number chosen is in accordance with that fixed by Varro, and with the exception of the _Cumaean_, who seems to take the place of the _Cimmerian_ in his list, the choice of prophetesses is the same. For the purpose of study, let us begin at the Western door; and commence with _The Delphic Sibyl._