The church is preceded by a 13th-century portico, in whose architrave was once a mosaic frieze with gilded letters. Today only few fragment of the latter can be seen. Two central piers support a rounded arch, in which is the writing ?Gloria in excelsis Deo??, while another inscription at the top contains the name of the portico's designer, "IACOBUS CIVIS ROMANUS" ("James, citizen of Rome") and the date of execution (1210). The central and final piers of the portico are decorated with the marble symbols of the Four Evangelists, while in the middle of the arch is a lamb, symbolizing Jesus Christ.
