San Carlo al Lazzaretto is a small Renaissance style octagonal church now in largo Bellintani Fra Paolo, number 1 in the quartiere Porta Venezia of Milan.
Its present situation, amidst crowded 19th and 20th century apartment blocks, has little relationship to its original placement, in the central park of a massive rectangular cloister-like 15th-century leprosarium (Lazaretto).
The church, once called Tempietto di Santa Maria della Sanità or San Carlino, escaped the late-nineteenth century demolition of the Lazzaretto.
During the Cisalpine Republic, the architect Giuseppe Piermarini was commissioned to transform the church into a secular Temple of the Nation (Tempio della Patria).
[3] Because of the vibrations produced by the underground train under viale Tunisia which have damaged the dome the church has been subject to studies to reinforce its structure.