The only remaining side apse is partly visible at the right. The crypt, and subsequently the presbytery, are more elevated than in other Romanesque buildings. The crypt has two halls with cross vaults, above which, originally, were two ambons: today only part of the left one remains, with a marble eagle which once supported the lectern. The church is known for the frescoes which cover the nave's walls and the apse. The latter are likely earlier than the former, as testified by the different style. The apse frescoes show two bands of pictures with animals and vegetable motifs. They are surmounted by a praying Jesus within an almond frame. Jesus is wearing sandals, an uncommon feature of such depictions. He is flanked by two old men, the prophets Jeremiah and Ezekiel, behind whom are the two archangels Michael and Gabriel and two crowds. The lower walls of the apse show a short cycle of stories of St Vincent of Saragossa. The fourth panel features St Aribert offering a model of the church to God: the upper part of this scene is now at the Pinacoteca Ambrosiana of Milan. Next to the church is the contemporary Baptistry of St John, which was built at the same time. Its plan is inspired by that of the 9th century Santa Maria presso San Satiro in Milan, although in a simplified form: a cruciform shape with a square hall limited by four isolated columns and four perpendicular arches, and four semicircular niches. The western niche opens to the interior, from which stairs lead to the matronei (tribunes in the upper floor), which are not present in San Satiro. The interior ends with a dome, externally covered by an octagonal drum with four windows and small arches.