Basilica of Santi Quattro Coronati

This fortified basilica near the Lateran feels more like a small monastery than a city church, with high walls, a defensive tower, and a hushed cloister of paired columns at its heart. Rebuilt in the twelfth century after fire damage, it retains a serene inner courtyard and a chapel decorated with a remarkable thirteenth-century fresco cycle showing the legend of Constantine and Pope Sylvester. Cloistered nuns still occupy the complex, and access to the frescoed Chapel of San Silvestro is arranged through a turntable window.