Sant'Angelo in Formis, Medieval basilica and archaeological site in Capua, Italy.

Sant'Angelo in Formis is a medieval basilica and archaeological site near Capua built on the ruins of a Roman temple. The church has three naves separated by ancient columns and a bell tower beside an entrance portico with five arches.

The church was first documented as ad arcum Dianae, built over a Roman temple to Diana whose remains were found in 1877; the basilica follows its perimeter. Under Bishop Peter I of Capua (925–938) it was given to the monks of Montecassino. Prince Richard of Capua returned it to them in 1072, and Abbot Desiderius rebuilt it between 1072 and 1087, commissioning the frescoes. In the 12th century the portico was redone and the bell tower rebuilt after a collapse.

The name replaced the earlier ad arcum Dianae, "near the Arch of Diana". Its origin is disputed: one reading links the Latin forma to a conduit or spring, while another, considered unlikely, derives it from informis, "shapeless". The church is dedicated to St Michael the Archangel, a devotion widespread among the Lombards from the late 6th century.

The church sits on the western slope of Mount Tifata and is reached by a winding road that climbs from Capua. Visitors should wear comfortable shoes, as the path from the parking area to the entrance rises gently.

The apse preserves an 11th-century fresco cycle that ranks among the best-preserved medieval wall paintings in southern Italy. The scenes follow a clear theological order from the Last Judgment down to episodes from the Old and New Testament.