Beyond a 1613 facade by Giovanni Fontana, this little church, whose founding dates from before the 8th century, retains a few good late-Renaissance paintings. The second altar on the right has a Guido Reni Circumcision (1636), and beyond it is a severely darkened Il Guercino Martyrdom of St. Bartholomew. The high altar is a fair baroque job by Giuseppe Mazzuoli, and as you leave take a good look at Domenico Beccafumi's Mannerist Nativity on the third altar of the left aisle.
Just to the facade's left is the Renaissance Loggia del Papa (1462), built for Pope Pius II. When you exit San Martino, head left down Via delle Scotte to no. 14 to see the 18th-century Synagogue, a remnant of the Jewish ghetto that existed behind the Campo from 1571 to 1796. It doesn't keep regular hours, but you can ring the bell anytime outside the Sabbath for a tour costing 3€ per person. For information, call tel. 0577-284-647.