The image-makers of the thirteenth century had not always taken into account the ideas expressed by their precursors; they had repeated them, expressing them from their own point of view in their personal tongue; thus, for instance, they had introduced a second version of the signs of the seasons and of the zodiac. The sculptors of the twelfth century had made a calendar in stone on the western front; those of the thirteenth did the same in the right-hand doorway of the north porch, justifying this reduplication of the subject on the same church by the fact that the zodiac and the seasons may in symbolism have several interpretations. According to Tertullian the death and new birth of the circling years afforded an image of the Resurrection at the end of the world. According to others the Sun, surrounded by the twelve Signs, was emblematic of the Sun of Justice surrounded by his twelve Apostles. The Abbe Bulteau sees in these stony calendars a rendering of the passage in which St. Paul declares to the Hebrews that "Jesus is the same yesterday, to-day, and for ever," while the Abbe Clerval gives this simple interpretation: that all times belong to Christ, and are bound to glorify Him. "But this is a mere detail," said Durtal to himself. "In the whole structure of the cathedral itself we can trace two-fold purposes. "The architectural mass of Notre Dame de Chartres as a whole may be divided, externally, into three great parts, as indicated by the three grand porches. The western or royal portal, which is the ceremonial entrance to the sanctuary, between the two towers; the north porch on the side next the bishop's palace, beyond the new spire; the south porch, flanked by the old spire. "Now, the subjects represented on the royal front and in the south porch are identical. Each glorifies the Triumph of the Incarnate Word, with this difference: that on the south porch Our Lord is not exalted alone as He is on the west front, but in the person also of the Elect and of His Saints. If to these two subjects, which may be considered as one--the Saviour glorified in Himself and in His Saints--we add the praises of the Virgin set forth in the north front we find this result: a poem in praise of the Mother and the Son as declaring the final cause of the Church itself. "By studying the variations between the south and west fronts we perceive that, though in both Jesus is shown in the same act of blessing the earth, and though both are almost exclusively restricted to illustrating the Gospel, leaving the scenes of the Old Testament to the arches on the north, they differ greatly from each other, and are no less unlike the portals of all other cathedrals. "In total disagreement with the mystic rituals observed almost everywhere else--at Notre Dame de Paris, at Bourges, at Amiens, to name but three churches--the Last Judgment, which is seen on the main entrance of those basilicas, is at Chartres relegated to the south porch.