St. Denis' abbatial was an object lesson in the new art, and the bishops returned to their dioceses to emulate it. Two of Suger's personal friends, the bishops of Noyon and Senlis, were the first to rebuild their cathedrals. Already during the Romanesque stage the cathedral of Sens had been initiated; it now was to be carried on according to the new system of building. At Laon was begun a splendid Gothic edifice. At Soissons, a new cathedral was started by that masterpiece of Primary Gothic, the transept's southern arm. And many a lesser church now rose: the collegiate at Braine, the abbey church of St. Leu d'Esserent, and two abbatials in Champagne as imposing as cathedrals, St. Remi at Rheims, and Notre Dame at Châlons-sur-Marne. Also in Champagne is the Primary Gothic church of St. Quiriace at Provins. The cathedral of Paris was also begun in the primary stage of the national art. But Notre Dame of Paris must have a chapter to itself. Before its main parts were completed, Gothic architecture had reached its culminating point. With it ended the primary group and opened what we shall call the Era of the Great Cathedrals, though let it be remembered that all such divisions are arbitrary and made use of merely for clearness. From its first assured steps to its apogee, from the middle of the XII century to the middle of the XIII, the sequence of Gothic architecture is welded too logically to be defined by cut-and-dried nomenclature. During the XII century, the Gothic cathedrals retained Romanesque features, such as deep tribunes over the side aisles, which gave them a wall elevation in four stories--pier arcade, tribune, triforium (to veil the lean-to roof over the tribune), and clearstory. At first it was common usage to encircle the clustered shafts at intervals with stone rings, but by the XIII century the desire for an unbroken ascending line had grown stronger, and the employment of such horizontal bands died out. The simultaneous use of both round and pointed arch is found in all five of these Primary cathedrals; but after the opening of the XIII century, semicircular and equilateral arches rarely were used at the same time in a church. Slowly, as if with reluctance, the new architecture dropped favorite traits of the old school. Sculpture continued longest faithful to Romanesque traditions. Noyon, Senlis, Sens, Laon, and Soissons--it seems rash to treat of such a bevy of churches in one chapter, when students have made a single cathedral their life work. The passing traveler is encouraged by one fact: each big French church, once seen, remains a clear-cut memory, for each possesses a distinct personality. To confuse one cathedral with another is impossible.