Set amid the greenery of the Celian Hill, this church wears its Baroque facade proudly. Dedicated to St. Gregory the Great (who served as pope 590–604), it was built about 750 by Pope Gregory II to commemorate his predecessor and namesake. The church of San Gregorio itself has the appearance of a typical Baroque structure, the result of remodeling in the 17th and 18th centuries. But you can still see what's said to be the stone slab on which the pious St. Gregory the Great slept; it's in the far right-hand chapel. Outside are three chapels. The right chapel is dedicated to Gregory's mother, St. Sylvia, and contains a Guido Reni fresco of the Concert of Angels. The chapel in the center, dedicated to St. Andrew, contains two monumental frescoes showing scenes from the saint's life. They were painted at the beginning of the 17th century by Domenichino (The Flagellation of St. Andrew) and Guido Reni (The Execution of St. Andrew). It's a striking juxtaposition of the sturdy, if sometimes stiff, classicism of Domenichino with the more flamboyant and heroic Baroque manner of Guido Reni.