The choir is situated to the rear of the altar, a place of prayer for the community of monks who lived in the cloisters - now a part of Università Cattolica del Sacro Cuore, which extends behind the Basilica. Another community - the canons - once occupied the cloister to the left of the Basilica. Hence, the two bell towers, representing the two communities.
From here, the rear of the golden altar can be seen, with the section dedicated to the life of St. Ambrose, an inspiration for the consecrated who sat here during the liturgy.
Looking upwards, admire the ornate apse mosaic depicting the Redeemer between Saints Gervasius and Protasius. The bodies of the two holy martyrs are placed beneath the altar, next to the body of Sant'Ambrogio.