Traces of Roman and Paleo-Christian architecture are still clearly recognizable in the structure of this church located on Corso di Porta Ticinese. The square in front of the church is dominated by a bronze copy of the statue of Emperor Constantine and sixteen Roman Corinthian style columns.
The latter are the remains of a 3rd century temple. The church was built at the end of the 4th century. After innumerable incidences of fire and collapse of the structure the church was restored in 1632 to the form in which we see it today.
The architectural styles of different periods are mixed: the primitive Paleo-Christian structure prevails but it has been modified by Romanesque and late 16th century features.
It has a mighty and imposing early 17th century dome and a 19th century facade. Around the interior walls of the basilica are the beautiful chapels of Sant’Aquilino, Sant lppolito and San Sisto plus Paleo-Christian mosaics and frescos from various periods.