THE CONTINUED DISAGREEMENT among art historians over the date of the founding of S. Lorenzo Maggiore is due in part to the absence of contemporary written testimony, and in part to apparent contradictions posed by the only other evidence available-archaeological and circumstantial. Dialogue is inhibited by a tendency of those treating the problem to explain these contradictions away, to minimize or even ignore them. It is the purpose of the present study, therefore, to review the evidence for the date of S. Lorenzo in some detail; to find what contradictions exist and to analyze them; and to suggest some means of resolution. S. Lorenzo and its chapels were erected just outside the ancient city wall of near the Porta Ticinensis, and fronted on the homonymous road to Pavia (Fig. I). Excavations and a minute archaeological study, conducted in the 1930s, made it possible to distinguish the early Christian nucleus of the church complex from its later additions, alterations, and repairs.1 The components of the original plan are: the tetraconch central building with its galleried ambulatory and the four towers between its exedrae; the three monumental chapels which open off the conches: S. Aquilino to the south, S. Ippolito to the east, and S. Sisto to the north; two apsed rooms, since destroyed, which flanked S. Ippolito; and a large atrium with an imposing streetside colonnade (Figs. 2, 3, 4). The early Christian fabric can still be discerned, on the ground floor level at least, in the perimeter walls of the tetraconch and in its four great corner piers; in the lower parts of two towers and the full height of a third, the northeast; in the walls of the chapels of S. Sisto and S. Ippolito; and throughout the octagon of S. Aquilino, which preserves even its early Christian cloister vault. An important aspect of the excavations just cited was the study of the foundations, which yielded a relative chronology for the various elements of the church complex. The foundations under the rising walls, piers and colonnades of the main quatrefoil are built with large cut blocks of granite and ceppo (a kind of conglomerate) and pieces of cornices and friezes in a harder stone called serizzo (gneiss). Apparently the remains of some monumental, demolished building, these ceppo and serizzo blocks appear also in the foundations of S. Ippolito, and over 6ooo of them were used in the construction of the large platform, first discovered in 1910 o, which underlies the chapel of S. Aquilino (Fig. 5).2 The foundations of S. Sisto, on the other hand, do not contain any of these large blocks and architectural fragments; they are built with smallish blocks ofceppo and also differ from the other foundations in their depth and form. Thus it is only logical to posit that S. Lorenzo and S. Ippolito, with identical foundations bonded together, were built first, while S. Aquilino, resting on foundations which comprise the same materials but are not bonded to those of the basilica, was built in the same campaign, if perhaps in a later phase.3 S. Sisto, This study originated in 1968 in a seminar with Prof. Richard Krautheimer, whose continued interest and advice have been invaluable throughout its subsequent transformations. Additional research in Italy was made possible by a Fulbright-Hays Grant and by other generous grants from the S. H. Kress Foundation, the National Gallery in Washington (a Chester Dale Fellowship), and the American Academy in Rome. To all these people and institutions, warmest thanks. The photographs for Figs. 2 and 5 were obtained through the kindness of Prof. M. Mirabella Roberti. I. See A. Calderini, G. Chierici, and C. Cecchelli, La Basilica di S. Lorenzo Maggiore in Milano (Milan [1952]). What follows here is drawn from the information on pp. 85-12o. On the narthex, which may or may not be an original component, see Mario Mirabella Roberti, Una nota sul nartece di San Lorenzo, Studi in onore di Carlo Castiglioni (Fontes Ambrosiani, xxxii, 1957), PP. 475ff. 2. For the early excavations under S. Aquilino, directed by A. Annoni, see R. Soprintendenza ai Monumenti della Lombardia, Relazione intorno alle ricerche ai ritrovamenti ed ai lavori fatti nella zona archeologica di S. Lorenzo in Milano dall'ottobre 191o al dicembre 1911 (Milan, 1913), esp. pp. ix-xi, 12-23. 3. For a detailed discussion of the date, as well as of the original function of S. Aquilino see my article, 'Capella reginae': S. Aquilino in Milan, forthcoming in Marsyas, xv.