Nestled in a quiet corner of Trastevere's focal square, this is said to be the oldest church dedicated to the Virgin Mary in Rome. In its original form, it dates to the early 3rd century, but a major 12th-century makeover saw the addition of a Romanesque bell tower and glittering facade. The portico came later, added by Carlo Fontana in 1702. Inside, the 12th-century mosaics are the headline feature.
In the apse, look out for Christ and his mother flanked by various saints and, on the far left, Pope Innocent II holding a model of the church. Beneath this are six mosaics by Pietro Cavallini illustrating the life of the Virgin (c 1291).
According to legend, the church stands on the spot where a fountain of oil miraculously sprang from the ground. It incorporates 21 ancient Roman columns, some plundered from the Terme di Caracalla, and boasts a 17th-century wooden ceiling.