other monastic buildings at Cluny has left a great lacuna in the history of mediaeval ecclesiastical and conventual architecture. In the late tenth century and throughout the eleventh century the group at Cluny was the model and set the standard, being the focus and center of a highly organized monastic system which ultimately comprised about 1450 dependencies. At the time when the Congregation of Cluny was at the summit of its power and effectiveness the great third church (Fig. 1) was built as a sort of capitol church, or, to use another figure, as the spiritual hearth of the entire Cluniac group of monasteries which then extended from Spain into Middle Europe, and even possessed a few priories in the Near East. In architecture the work of the abbey was very important. In the period of its greatest influence (which was inter-regional) monastic architecture was of primary rank because the monasteries played so vital a role in the economic, intellectual, spiritual, and governmental life of the time. Three successive great abbots of Cluny--Mayeul (948-994), Odilo (994-1049), and Hugh (1049-1109)were interested in good building. They traveled to Rome and over wide areas in Western Europe. Personally or by directive they brought about the erection of at least four hundred churches and several thousands of other, less spectacular, monastic buildings. The building art of all Western Europe was the gainer because of the high ideals in this work. Abbot Hugh was interested in Roman, in Byzantine, and in Moslem art, specimens of which he saw during his sixty years of journeying on behalf of Cluny; the enrichment of Romanesque architecture during his lifetime unquestionably owes something to this fact, and the same thing may, of course, be said of sculpture and painting. What we have lost at Cluny itself (Fig. 2) is a great architectural paradigm which, if it still existed, would bring our ideas of both tenthand eleventh-century architecture into much sharper focus. If the imperial Cathedral of St. Sophia in Constantinople had been destroyed we would be in the same position with respect to Byzantine architecture, and it would be almost impossible to gain a clear idea of the potentialities of the Byzantine style at its culmination. The buildings at Cluny possess, in their way, the same relative importance for their own epoch. Cluny was indeed a monastic empire. Popes, kings, emperors, and saints figured prominently among its multitudes of visitors in mediaeval times. So extended and widely ramified were Cluniac affairs that despite voluminous publications beginning in the seventeenth century, no general history of the abbey has as yet been achieved, and the same thing is true for the buildings of the mother house. By charter of September 11, 909 (not, as usually written, 910), the monks were given a Gallo-Roman villa, by then largely Carolingian in construction. They soon started to build and rebuild for themselves, and with negligible gaps they continued their progressive reconstruction of the monastery until, in 1790,, the general expropriation of monastic properties put an end to a final huge project of rebuilding which had been under way since about 1750. Even without the difficulties introduced by the incessant demolitions and reconstructions, the architectural historian's task would be enormous at Cluny because of the great age of the earlier structures, and the ever-increasing scale of the later ones. The first church (c. 910-27) was about 120 feet long; the second church (c. 950-81 and later) was about 200 feet long; the third church (1088-1120 and later) ultimately reached a length of almost 615 feet English measure (Figs. 3 and 4). The monastery buildings in the reconstruction of 9911043 were based on a 300-foot square (3342% feet English measure), but in the end the western building alone consisted of ten wings aggregating about 1744 feet (nearly a third of a mile) in length, with eleven towers of some size in addition to the 135-foot pair at the facade of the church narthex, which was functionally related to the western building. There was a concurrent development at the south and east in the monastery group. It will surprise no one that a thorough study of this group has entailed over thirty years of work by the present author and several collaborators, especially Frederic Palmer and Helen Kleinschmidt. During this long period, and with the aid of munificent grants from the John Simon