The lower part of the apse dates from the twelfth century, with its radial chapels and, above, the little semi-circular windows of the galleries. The upper part of the church belongs to the sixteenth century. The rich façade of the transept also dates from the sixteenth century. [Illustration: SOUTH FAÇADE OF THE CATHEDRAL] [Illustration: THE CATHEDRAL: SOUTH FAÇADE OF TRANSEPT] The opposite view shows the detail of the +SOUTH FAÇADE OF THE TRANSEPT+ designed by Pierre Chambiges, son and pupil of Martin Chambiges. The latter worked on the Cathedrals of Beauvais, Sens and Troyes, and his son drew inspiration from his work for the execution of that entrusted to him at Senlis; this explains the great resemblance that various portions of those edifices bear to one another. In comparing the south portal with the western façade one notes the development of Gothic architecture from the twelfth century, when its restraint and simplicity of line still recalled Roman art, to the sixteenth century, when rich, flamboyant decoration flared in its final splendour, making way for the art of the Renaissance that the Italian wars brought into fashion. [Illustration: THE CATHEDRAL: NORTH FAÇADE OF TRANSEPT] The appearance of this fine _ensemble_ is spoilt by the adjacent polygonal vestry erected on its right, which was rebuilt in the nineteenth century. A part of it can be seen in the above photograph; though one can judge still better of its ugly effect from the photograph on the preceding page. +The north façade of the transept+ is, in its general arrangement, the same as that on the south, but it is less richly ornamented. On the pediment which surmounts the entrance are carved the salamander and the "F" of Francis I. On that of the south are the arms of France. The tourist should not fail to look at the north side of the Cathedral, which is very picturesque. On the north tower the marks of German shells are still to be seen. They are clearly shown in the photograph (_foot pp. 46-47_). [Illustration: PLAN OF CATHEDRAL E, stairs leading to galleries. G, chapel of transept (vault with pendentives). M, aisles of choir. O, radial chapels of the twelfth century (modern windows).] [Illustration: SECTION OF CATHEDRAL A, roof of nave. B1, B2, B3, B4, transept. C, piers supporting the vault on the nave by means of flying buttresses. D, first aisles of nave and ambulatory. G, second aisles of nave. T, galleries running round the church.] [Illustration: GALLERIES OF THE CATHEDRAL] [Illustration: HANGING BOSSES] The galleries of the cathedral are among the most beautiful in France. The above view, taken from the choir galleries which overlook the southern part of the transept, shows those of the nave in enfilade. _In order to visit these galleries the key must be obtained from the vestry._