No people outside of France better understood and developed Gothic art than the English. Their claim to priority is based on the date of the cathedral of Durham, whose choir-aisle diagonals Mr. John Bilson says are as early as 1093. Since those diagonals show no hesitation, they must have been preceded by others. Where in England are there to be found the earlier trials? The English claim is practically a Norman one, and Normandy's experimental work in Gothic vaultings remains to be traced. Rivoira claims that Lombard influences predominated in the formation of Normandy's Romanesque school. Can the Norman be said to have discerned in diagonals their immense possibilities any clearer than had the Lombard? Those among the French archæologists who have disputed the Norman claim to priority say that the principal span of Norman and English churches was covered with timber roofs far into the XII century. We know that the Gothic vaulting of the two abbey churches of Caen were XII-century additions, and M. de Lasteyrie thought the same was true of Durham, though Mr. Bilson has convinced MM. Enlart and Lefèvre-Pontalis that Durham's choir-aisle vaults are an original part of the cathedral begun in 1093. Not till 1174, when Guillaume de Sens began Canterbury Cathedral, did French Gothic architecture, in its plenitude, appear in England. The question of priority remains an open one. It might almost be said that vaulting with intersecting ribs began to appear here and there simultaneously, that if it had not cropped out in the Ile-de-France, it would have appeared in Normandy, or vice versa. And not long after them, the builders in Burgundy and Anjou began to use it. Before 1150, isolated samples of the Gothic rib vault appeared at Vézelay, Poitiers, Bordeaux, Quimperlé, Moissac, St. Gilles, Marseilles. The hour was ripe for the solution. Gothic architecture was the spontaneous invention of French builders at the dawn of the XII century, at a time when the poetry of France was imposing itself on the whole of Europe. _L'oeuvre initiale_ will never be known. However, there was a region where the early use of the ogival vault was not accidental, but systematic, one spot in the heart of France where it immediately made a school, since there it found no strong earlier traditions to overcome, where it became a living organism and went through a succession of logical developments until it had taken on the main characteristics of the new art. There is one center from which Gothic architecture spread out with slow, sure march into the neighboring regions. In the Ile-de-France, all the trials were summed up and developed by Abbot Suger at St. Denis. From 1140 to 1144 he wedded definitely the pointed arch with the diagonal rib.