Why is there only one angel on the facade of the church of Sant' Andrea della Valle?
The angel is the work of Giacomo Antonio Fancelli (1619-71), whose brief was to carve two angels. The story goes that no less a figure than Pope Alexander VII (r. 1655-67) found fault with Fancelli's angel. The temperamental sculptor took offence and declared in a huff, that, if the Pope wanted a second angel, he would have to carve it himself!
Sant' Andrea della Valle was begun in 1591 and financed by Cardinal Alfonso Gesualdo di Conza for the Order of the Theatines. The initial architects were Giacomo della Porta and Pier Paolo Olivieri. Work was continued by Carlo Maderno, who built the dome, the highest in the city after that of the Basilica di San Pietro. It is decorated with a fresco of the Glory of Paradise (1621-25) by Giovanni Lanfranco.
A tiny church dedicated to Saint Sebastian originally occupied the site, but in 1582 Donna Costanza Piccolomini, who was the duchess of Amalfi, bequeathed money and property to the Order of the Theatines. Her only stipulation was that a much larger church, and one dedicated to Saint Andrew (patron saint of Amalfi), should be built on the site. Inside the church there are funeral monuments to popes Pius II (r. 1458-64) and Pius III (r. 1503), both members of the Piccolomini family.
The Congregation of Clerics Regular of the Divine Providence was founded in 1524 by, amongst others, San Gaetano and Giampaolo Carafa, who later became Pope Paul IV (r. 1555-59). The Congregation came to be known as the Theatines, because Carafa, its first Superior General, was Bishop of Theate (modern day Chieti). The Order’s objective was to instil virtue in the laity and to reform the clergy.