Alexander Hamilton U.S. Custom House ca. 1910

Cass Gilbert’s design for the Rotunda of the U.S. Custom House at Bowling Green called for an elliptical, skylit dome spanning 85 by 130 feet. The size and shape of such a structure posed substantial engineering challenges. Guastavino Sr. devised a solution consisting of a pair of thin tile domes—one inside the other—supported by two elliptical steel rings: one at the top of the supporting walls and another at the skylight’s perimeter. Ornamental plaster covers the inner dome, obscuring the tiles from view.