According to Michael Klepper and Robert Gunther in an article in American Heritage, Andrew Carnegie was second only to John D. Rockefeller as the richest American who ever lived. Having made his fortune in steel, Carnegie built a mansion, in 1899-1903, in a sparsely settled and not fashionable part of the Upper East Side, on the southeast corner of Fifth Avenue and 91st Street. With Central Park across the avenue, and open lots all around, the setting must have seemed like a country retreat. Soon, however, Carnegie began to sell lots he owned across 91st. The purchaser of two lots, just in from Fifth Avenue, was Emily Vanderbilt Sloane. She was the granddaughter of Cornelius Vanderbilt (Messrs. Klepper and Gunther’s third richest American), and bought the lots so as to erect houses for two of her daughters, Mrs. John Henry Hammond and Mrs. James A. Burden.

But the neighborhood’s grandest house, grander even than Carnegie’s, was that of Otto Kahn, who also purchased his lot from Carnegie.

Kahn, a German Jewish immigrant and a partner in Kuhn, Loeb, became one of the country’s most successful investment bankers. He and his wife, Addie, were also among the city’s greatest patrons of the arts. Kahn practically owned the Metropolitan Opera Company and single-handedly kept it afloat in lean times. His other beneficences ranged from support for Diaghilev’s Ballets Russes to the restoration of the Parthenon.

The Fifth Avenue house is a showstopper. It’s a Medicean palazzo, turned in on itself with an external show of impregnable strength. While to say as much may suggest poor urbanism, this house succeeds on the same terms as York & Sawyer’s fortress-like Federal Reserve Bank on Liberty Street. That is, the house has such a finely wrought exterior that, far from offending the pedestrian, it delights.

Note especially the luscious stone – the same French limestone that Horace Trumbauer used for the Wildenstein Gallery on 64th Street. The dates of Kahn’s house are unusual: 1913-8. This tells us that the stone Kahn and his architects – C.P.H. Gilbert and J. Armstrong Stenhouse – specified was impossible to secure as France went to war. Kahn waited. (Gilbert also designed the mansion of another Kuhn, Loeb partner, Felix Warburg, a block north on Fifth Avenue.) Though it’s hard to see, the Kahn house’s internal courtyard is one of the most stunning places in New York.

Carnegie’s house, by Babb, Cook & Willard, is by contrast an unprepossessing affair, lovely to be sure, but proclaiming splendor by having something very rare in Manhattan: a lawn. (Great splendor exists within, as well.)

The Carnegie house is now the Cooper-Hewitt Museum. The Kahn house and the Burden house belong to the Sacred Heart Sisters, who came to New York in the 1840s as part of Archbishop Hughes’s expansion of Catholic institutions to serve the immigrant city. In 1934 they came to steward the Italian Renaissance-style home of a great German Jewish financier. That speaks volumes about the immigrant synergies that have made New York great.