=Hôtel des Invalides.=--The latter is vast but truly barrack-like, with tedious repetition of the orders; but is celebrated for the stately grace of the dome. This surmounts the church that is in the form of a Greek cross, the angles being filled with chapels, so as to make the complete plan a square. The exterior design of the dome includes a high drum, pierced with windows, between which project eight coupled columns that form buttresses. These terminate in carved corbels, which reinforce a smaller drum, with round topped lights. From this springs the dome; the grace of its curve being echoed in the airy cupola whose roof diminishes in concave curves to a soaring point. The somewhat excessive height of the exterior needed on the inside very considerable reduction, in order to bring it into proportion with the rest of the interior. This the architect accomplished by erecting beneath the wooden shell of the outer dome two interior ones, a middle and a lower one, independently constructed. The lower, which rises immediately above the lower drum, has a large circular opening, through which is visible the decorations painted on the middle dome, which rests upon the upper drum and is lighted by its windows. The whole structure is supported upon four large piers, which, as in S. Paul’s, London, are pierced by arched openings, leading, in the case of the Invalides, into the four angle chapels. Another instance of a triple dome occurs in the Church of =S. Geneviève=, better known as the =Pantheon=, which we shall refer to later in connection with the Classic revival, although its construction, extending from 1755 to 1781, occupied a considerable part of the Rococo period. =Rococo.=--The Rococo is marked by a further decline into dry and pedantic formality in the use of the orders, which, however, in time produced a reaction toward a more intelligent, if uninspired, observance of the principles of classic design. It appears in the façade added to the Church of =S. Sulpice= in 1755 by the Italian, Servandoni. This comprises a Doric portico, supporting an Ionic arcade, above which, at the extremities, rise turrets in two tiers of orders. Other examples which mark the end of the reign of Louis XV will be referred to in the subsequent chapter on Classic Revival.