According to legend, Santa Maria del Popolo occupies the site of a garden in which hated Emperor Nero was buried. The site was still believed to be haunted by demons 1,000 years later; in 1099 Pope Paschal II built a chapel there to dispel them. Nearly four centuries later, beginning in 1472, Pope Sixtus IV rebuilt the chapel as a church, financing it by taxing foreign churches and selling ecclesiastical jobs.
In the apse are, unusually for Rome, stained-glass windows, a northern touch created by French artist Guillaume de Marcillat in 1509. The apse itself was designed by Bramante, while the choir ceiling and first and third chapels in the right aisle were frescoed by Pinturicchio, the favourite artist of the Borgias. In Pinturicchio's exquisite works (1508-10), the Virgin and a host of saints keep company with some very pre-Christian sibyls. Most intriguing is the Chigi Chapel, designed by Raphael for wealthy banker Agostino Chigi. The mosaics in the dome depict God creating the sun and the seven planets, and Agostino's personal horoscope: with binoculars you can just about make out a crab, a bull, a lion and a pair of scales.
The chapel was completed by Bernini, who, on the orders of Agostino's descendant Pope Alexander VII, added the statues of Daniel and Habakkuk. The church's most-gawped-at possessions, however, are the two masterpieces by Caravaggio to the left of the main altar, in the Cerasi Chapel. On a vast scale, and suffused with lashings of the master's particular light, they show the martyrdom of St Peter and the conversion of St Paul. To the left of the main door is a memorial to 17th-century notable GB Gisleni: grisly skeletons, chrysalids and butterflies remind us of our brief passage through this life before we exit the other end.