The Basilic of St. Lorenzo stands on an artificial hill. The building, a central plan, is surrounded by four towers and three smaller octagonal buildings. Around the central room runs an ambulatory surmounted by an upper gallery; on the side opposite the entrance, there was a chapel of a Greek cross, later dedicated to St. Hippolytus, the side of which opened a tradoantico quadriportico (late fourth century) with sixteen marble columns of Musso-Olgiasca, today strongly altered. Over the centuries, in fact, the columns were isolated from the body of the Basilica and exposed to threats of demolition. The chapel of St. Aquilino is the only part of the complex that has retained its original structure: an octagonal space outside, but inside articulated in semicircular niches, covered with hemispherical "umbrella" dome (typical technique of Ravenna, sixth century). Recent investigations have dated this chapel between the 390 and the 430, but the interpretation of the function of use is disputed between baptistery and mausoleum. Symmetrical to the chapel of St. Aquilino, lies St. Sisto, which houses the tombs of bishops. The entire basilica complex is made by recovery materials.