Spiral stair at the Cathedral of Saint John the Divine (begun 1892) in Manhattan demonstrates the spatial and structural complexities of some of the Guastavino tile vaults. The brilliance of the Guastavino system lies in the seamless integration of structure and finished surface. Each layer of tiles was offset from the adjacent layer to create an interlocking pattern, reminiscent of a woven basket. Such patterns help to distribute forces evenly throughout the structure, making it remarkably strong despite the thinness and lightness of the tiles. Photo © Michael Freeman, Courtesy of the Museum of the City of New York