The church of San Giovanni in Foro, located along the former Via Postumia, now Corso Porta Borsari, takes its name from its close proximity to the ancient Roman forum, now Piazza Erbe. The sacred Romanesque building (12th century) dedicated to the evangelist John was extensively remodelled and restored in the 20th century. The original structure had already been damaged by a fire in 1172, as indicated by an inscription on the south side. Facing west, the original façade was soon incorporated into the adjacent buildings. The main entrance, facing the street, is a Renaissance portal attributed to Girolamo Giolfino, with statues of Saints John the Evangelist, Peter and John the Baptist, and a lunette frescoed by Nicolò Giolfino depicting Saint John on the island of Patmos as he wrote the Apocalypse.
The interior of the single-nave church, preceded by an atrium with a truss roof, is largely 20th-century. The mosaic floor was created in 1932 by Ettore Fagiuoli, who drew inspiration from decorative motifs found in the Roman catacombs. Beneath the altar in the presbytery is a depiction of the Good Shepherd; on either side, two "cut" dolphins recall the sacrifice of Christ, while in the centre stands the sacrificed Lamb, symbolising Jesus crucified. Other elements include two fish, symbolising Christ, an amphora, referring to baptism, and grapes with two doves representing the Eucharist. The church houses a Madonna and Child signed in the early 14th century by the master sculptor Poia, encouraging visitors to pray for him.