San Costanzo, Minor basilica in Perugia, Italy.

San Costanzo is a parish church just outside Porta San Costanzo at the end of Borgo XX Giugno, on the spot where the saint was buried. Its present form dates to 1889, when Guglielmo Calderini rebuilt the main body in Romanesque Revival style, cladding the exterior in pink limestone from Assisi. The 12th-century apse and east wall survive, along with the original marble portal carved with vine tendrils, animals and a blessing Christ.

A first funerary monument to Saint Costanzo, the city's first bishop martyred near Foligno, dates to 178; a small church, perhaps San Martino in Ajole, later stood on the spot. In 1205 the priest Alessio enlarged and consolidated it at his own expense, and Bishop Viviano consecrated it. The present building was rebuilt entirely in 1889 to designs by Guglielmo Calderini, keeping the 12th-century apse and the marble portal.

The church is dedicated to Saint Costanzo, traditionally held to be Perugia's first bishop, martyred near Foligno under Marcus Aurelius. In 1825 a large procession with civil and religious authorities carried his relics back here from the basilica of San Pietro; they were placed in a purpose-built casket in the altar, together with an ampoule of his dried blood and a marble slab said to bear the imprint of his body.

The church stands just outside Porta San Costanzo at the end of Borgo XX Giugno, in Perugia's historic centre. Its north side is flanked by a travertine portico, once used as a market by local farmers, which shelters the entrance. The piazzale in front was levelled in 1997, making the approach flat and easy to walk.

The 1825 procession brought Saint Costanzo's relics back from the basilica of San Pietro; a purpose-built casket was placed in the altar, along with a vial of his dried blood and a marble slab said to bear the imprint of his body.