The parts which have survived of that other notable Benedictine establishment in Paris, St. Martin-des-Champs, are now comprised in the _Arts et Métiers_ establishment. Affiliated with great Cluny, St. Martin's priory was as like it, said Peter the Venerable, as seal is like signet. To-day in the ancient church is installed an exhibit of machinery. The beautiful hall, once the monks' refectory, and now a technical library, is thought to be the work of Pierre de Montereau. The slender pillars dividing it into two aisles, the well-carved capitals, the elaborate keystones, and the portal's foliage all belong to the golden hour of the national art. For the student it is the choir of the church (c. 1135), built by the prior who surrounded the monastery lands with walls (1130-40), which is of chief interest, for in it were taken marked strides in the advance of Gothic structure. Here first was attempted a double ambulatory, an idea which Suger within a few years was to carry out in its fulfillment at St. Denis. The Lady chapel, a lobed half dome--the sacred trefoil--developed further the ribbed apse first found at Bury (c. 1125); here the ribs are structural, not merely decorative. Like other monuments of the transitional hour, St. Martin used simultaneously intersecting ribs and groins, round and pointed arches. Its XIII-century nave was never vaulted. The third monument of the capital which shows other stumbling first steps of the national art is the little church of St. Pierre under the towering new basilica of the Sacred Heart on Montmartre.[89] Till the XII century there stood on the site of St. Pierre a church dedicated to St. Denis, for tradition said that the first martyr of Paris had here been interred until his relics were removed to the new abbey of St. Denis on the Roman road outside Paris. In the crypt, by St. Peter's, on Montmartre, it is said that the earliest Christians of the region held their rites. And to that hallowed spot has come many a soul to beseech enlightenment on the eve of some projected good work. Here, in 1534, St. Ignatius Loyola, St. Francis Xavier, and the first Jesuits passed a night in prayer and vowed themselves to God's service. Here came St. Francis de Sales before founding the Visitation Order, St. Vincent de Paul before founding the Lazarists, and M. Olier before he organized St. Sulpice. Ursulines and Carmelites also have memories with St. Pierre-de-Montmartre. A Benedictine priory was installed here by Louis VI and his queen, Adelaide, niece of Pope Calixtus II of the Capetian house of Burgundy. They began the present church as Romanesque, but soon the new system of vaulting was employed. Slowly but consecutively throughout the XII century St. Peter's church was built. Its oldest Gothic vault is the one over the section of the choir preceding the apse; the stout ribs have profiles like those which Abbot Suger was making about that same time in the forechurch of his abbatial.