Archaeological Park of Castelseprio, Archaeological park near Castelseprio, Italy

The Archaeological Park of Castelseprio preserves the ruins of the fortified castrum and its borgo, with walls nearly 2 m thick, a tall broken tower, and the remains of the Basilica of San Giovanni Evangelista, an octagonal baptistery, and the hexagonal church of San Paolo. A stone staircase with grass between the steps leads through the lower walls, and an information panel stands near the tower base.

Excavations show the site was occupied from prehistory, with an Iron Age necropolis near Santa Maria foris portas. The castrum Sibrium was founded in the 4th-5th century as a defence against Germanic migrations, at the crossing of roads between Como and Novara. It became a civitas under the Byzantines and Lombards, then a Carolingian county. In 1285-1287 Milan razed it during the war against the Torriani; Archbishop Ottone Visconti decreed its perpetual abandonment, though the churches were officiated until the 17th century.

The name "foris portas" is Latin for "outside the gates", as the church lay beyond the citadel walls. Its apse holds a fresco cycle of the Infancy of Christ inspired by the apocryphal Gospels, painted in three registers, the middle one interrupted by three arched windows. The cycle is read as anti-Arian, asserting the single human and divine nature of Christ.

The ruins stand on a plateau reached by broad stone steps with grass between them; the ground is uneven and partly overgrown. A tall information panel stands near the broken tower, and the excavated area is explored on foot. The Church of Santa Maria foris portas lies outside the walls, a short distance from the castrum.

The octagonal baptistery of St John the Baptist, built between the 5th and 7th centuries, keeps two baptismal fonts inside; scholars suggest they served different rites. Its small apse faces east. The font arrangement is a detail most visitors walk past on the way to the Santa Maria frescoes.