J. Pierpont Morgan was a ruthless financial wizard with superb taste, whose monument--the library designed by McKim, Mead & White in 1906--was a surprisingly restrained product of America's first gilded age. Still more astonishing in that country's latest era of obscene excess, the Morgan has been doubled in size without losing its distinctive personality. The Renzo Piano Building Workshop has wrought its customary magic in weaving together old and new, strengthening the sense of place, and opening up the new central court to views of the street on three sides. Visitors walking into this serene, light-filled atrium, or looking down from two upper-level balconies can savour the sensation of floating within a transparent bubble at the heart of the metropolis.

Nearly all museums have a compulsion to expand, to display more of their holdings and find room for new acquisitions, but also to accommodate ever-greater crowds and boost revenue. A happy few, like the Frick, stay small and are cherished for doing so. In contrast, the Museum of Modern Art abandoned its early role as a tightly focused shrine of the avant garde, and turned itself into an overpoweringly vast emporium with all the appeal of a convention centre. By choosing Piano, who cares as much for the sacred (contemplating art) as the profane (socialising, shopping and eating) and manages to keep the two kinds of space distinct, the Morgan avoided that fate.