In 450 they built the lovely Galla Placidia at Ravenna. It is a building essentially un-Roman; that is to say, the Romanism that clings to it is accidental and adds nothing to its significance. The mosaics within, however, are still coarsely classical. There is a nasty, woolly realism about the sheep, and about the good shepherd more than a suspicion of the stodgy, Graeco-Roman, Apollo. Imitation still fights, though it fights a losing battle, with significant form. When S. Vitale was begun in 526 the battle was won. Sta. Sophia at Constantinople was building between 532 and 537; the finest mosaics in S. Vitale, S. Apollinare-Nuovo and S. Apollinare-in-Classe belong to the sixth century; so do SS. Sergius and Bacchus at Constantinople and the Duomo at Parenzo. In fact, to the sixth century belong the most majestic monuments of Byzantine art. It is the primitive and supreme summit of the Christian slope. The upward spring from the levels of Graeco-Romanism is immeasurable. The terms in which it could be stated have yet to be discovered. It is the whole length of the slope from Sta. Sophia to the Victoria Memorial pushed upright to stand on a base of a hundred years. We are on heights from which the mud-flats are invisible; resting here, one can hardly believe that the flats ever were, or, at any rate, that they will ever be again. Go to Ravenna, and you will see the masterpieces of Christian art, the primitives of the slope: go to the Tate Gallery or the Luxembourg, and you will see the end of that slope--Christian art at its last gasp. These _memento mori_ are salutary in an age of assurance when, looking at the pictures of Cezanne, we feel, not inexcusably, that we are high above the mud and malaria. Between Cezanne and another Tate Gallery, what lies in store for the human spirit? Are we in the period of a new incubation? Or is the new age born? Is it a new slope that we are on, or are we merely part of a surprisingly vigorous premonitory flutter? These are queries to ponder. Is Cezanne the beginning of a slope, a portent, or merely the crest of a movement? The oracles are dumb. This alone seems to me sure: since the Byzantine primitives set their mosaics at Ravenna no artist in Europe has created forms of greater significance unless it be Cezanne. With Sta. Sophia at Constantinople, and the sixth century churches and mosaics at Ravenna, the Christian slope establishes itself in Europe.[10] In the same century it took a downward twist at Constantinople; but in one part of Europe or another the new inspiration continued to manifest itself supremely for more than six hundred years. There were ups and downs, of course, movements and reactions; in some places art was almost always good, in others it was never first-rate; but there was no universal, irreparable depreciation till Norman and Romanesque architecture gave way to Gothic, till twelfth-century sculpture became thirteenth-century figuration.