St. Peter’s as thus completed (Fig. 170) is the largest church in existence, and in many respects is architecturally worthy of its pre-eminence. The central aisle, nearly 600 feet long, with its stupendous panelled and gilded vault, 83 feet in span, the vast central area and the majestic dome, belong to a conception unsurpassed in majestic simplicity and effectiveness. The construction is almost excessively massive, but admirably disposed. On the other hand the nave is too long, and the details not only lack originality and interest, but are also too large and coarse in scale, dwarfing the whole edifice. The interior (Fig. 171) is wanting in the sobriety of color that befits so stately a design; it suggests rather a pagan temple than a Christian basilica. These faults reveal the decline of taste which had already set in before Michael Angelo took charge of the work, and which appears even in the works of that master. +THE PERIOD OF FORMAL CLASSICISM.+ With the middle of the 16th century the classic orders began to dominate all architectural design. While Vignola, who wrote a treatise upon the orders, employed them with unfailing refinement and judgment, his contemporaries showed less discernment and taste, making of them an end rather than a means. Too often mere classical correctness was substituted for the fundamental qualities of original invention and intrinsic beauty of composition. The innovation of colossal orders extending through several stories, while it gave to exterior designs a certain grandeur of scale, tended to coarseness and even vulgarity of detail. Sculpture and ornament began to lose their refinement; and while street-architecture gained in monumental scale, and public squares received a more stately adornment than ever before, the street-façades individually were too often bare and uninteresting in their correct formality. In the interiors of churches and large halls there appears a struggle between a cold and dignified simplicity and a growing tendency toward pretentious sham. But these pernicious tendencies did not fully mature till the latter part of the century, and the half-century after 1540 or 1550 was prolific of notable works in both ecclesiastical and secular architecture. The names of Michael Angelo and Vignola, whose careers began in the preceding period; of Palladio and della Porta (1541-1604) in Rome; of Sammichele and Sansovino in Verona and Venice, and of Galeazzo Alessi in Genoa, stand high in the ranks of architectural merit. [Illustration: FIG. 171.--INTERIOR OF ST. PETER’S, ROME.]