The sequence of the passing from Romanesque to Gothic is obscure, because there is a lack of definite dates. From 1110 to 1140, while the intersecting ribs were coming into use in northern France, such a vault was practically the only sign in an edifice of the new movement. The walls still were massive, the windows still were small and round-arched, the sculpture still was coarse and heavy. Then, as the transition advanced, the supports grew lighter, the profiles (those cross-section outlines of ribs, arches, capitals, and bases) grew purer, and the sculpture discarded Byzantine traditions and took nature as its model. French archæologists have thought that the use of diagonals came about first through the desire to hold up some groin vault, on the point of collapsing, which would seem a very sensible explanation, since the creative genius of the Ile-de-France seems dimly to have apprehended even in the first hour the stupendous possibility to be drawn from a member whose purpose was to concentrate force in order that other parts of the edifice might be relieved. From the initial hour began the evolution of the cardinal organ in the Ile-de-France. Whereas the Lombard architects looked on the diagonals as a mere contrivance, stubbornly keeping their eyes shut to the structural possibilities latent therein. The masons of the Ile-de-France at once began to profile their diagonals graciously, and even before the genius of Suger had coordinated, at St. Denis, all the foregoing progress of the nascent art, craftsmen had occasionally symbolized, as it were, the importance of the intersecting ribs by carving little caryatids for them to rest upon above the capitals; such figurines are to be seen in the Oise region at Bury and at Cambronne.[21] Mr. Arthur Kingsley Porter's idea is that the transitional period resolves itself into a series of experiments on the part of the builders to erect a vault with a minimum of centering, and he cites the hollow spires at Loches as an experiment to put up a stone roof without the use of any temporary substructure of wood, which apparently was costly.[22] He thinks that the earlier Gothic vaults were _bombé_ because that form facilitated construction without centering, and that the Lombards dropped their precocious diagonals after 1120, as soon as they had learned how to build domed groin vaults which required no temporary wooden substructures. What is of value in Mr. Porter's thesis is sure, in time, to pass into French currency; until a majority of French archæologists find his explanation better than their own it is permissible for us to agree with those who are telling the tale of their own national art.