Borromini began construction on another of his architectural masterpieces, the church of Sant'Ivo alla Sapienza in Rome, Italy, in 1642 for Pope Urban VIII. His curvilinear façade, bulging drum, and spiraling lantern are all eye-popping aspects of his design. But it is the extraordinary floor plan of the church which makes it unique – an equilateral triangle with semi-circular niches along its sides and corners cut off by inward swinging arcs.