In 1657 fragments of a demolished quattrocento monument from the choir were reassembled in the chapel in the form of two aediculae by Cardinal Flavio Chigi, the nephew of Pope Alexander VII, who was Cardinal-Priest of the basilica at the time.

The side walls of the windowless, hexagonal chapel are articulated by painted Corinthian pilasters decorated with tendrils, vases, flowers, animals, sphinxes, phantastic creatures and garlands on a yellow background, resting on a fake marble pedestal.

The shafts of the Composite pilasters are decorated with ecclesiastical symbols: different types of crosses, cardinal's hats, torches, wreathes, palm branches, lamps.

The white marble central slabs are flanked by dwarf pillars which are decorated with different types of shields and bunches of fruits, ears and flowers.

It was originally set up in the apse of the Old St. Peter's Basilica but a Dutch traveller, Aernout van Buchel glimpsed it in 1587 among various other discarded tombs and sculptures in the nave due to the ongoing demolition of the ancient church.

The monument was restored and transferred to the choir of the Basilica of Santa Maria del Popolo by his great-nephews in 1596 to which date the longer inscription on the base belongs.

[4] At the same time the Pallavicini family erected another tomb in the right aisle for a long deceased member of their house, Cardinal Giovanni Battista Pallavicino.

The pilaster panels are covered with an elaborate ornamental decoration starting with tripods and terminating in crosses; the Corinthian capitals feature dolphins.

Similarly to the tomb of Antoniotto Pallavicini, the large monument didn't fit into the frame of the earlier painted architecture although it was designed for its present space from the beginning.

The sculptor of the sepulchre remains unknown but stylistically the tomb belongs to the group of Michelangelesque monuments very common in Rome in the decades following the death of the great artist.

As Enrico Parlato described it shows "a frozen and ′vacuumed′ Michelangelism in the dilatation of the space and the reduction of the ornament, the architectural idea coherently represented in sculpture in the austere bust of the deceased.

The realistic portrait bust of the deceased is set in an oval niche and a Latin inscription says: EXPECTO DONEC VENIAT IMMUTATIO MEA (I wait, till my change comes, Job 14:14), a reference to resurrection.

"[6] The slab is framed by a wide band of swirling oak branches, a symbol of the Della Rovere family, and a visual reference to the patron of the bishop, Pope Sixtus IV.

The Latin inscription also mentions the Pope: "Ioannem de Montemirabili hic sepultum, intelligentia apostolicum abbreviatorem, fides referendarium secretum, probitas Sixto IV.

"[7] (Ioannes de Montemirabilia is buried here, intelligence made him abbreviator apostolic, faith secret referendary, probity the familiar of Pope Sixtus IV., religion the Bishop of Vaison, died as a septuagenarian on 4 June 1479.

The menacing sky with the dense clouds and the simple log cross by the side of the two embracing, vivacious little angels alludes to the earthly fate of Jesus.

The slab of the ledge is decorated with a finely carved relief of the Sudarium and an almost invisible ornamentation of candelabra, oak leaf festoons, ribbons and scallops.

On the bases of the stone frame of the altarpiece there are two reliefs depicting the coats-of-arms of Cardinal Francesco Abbondio Castiglioni (left) and a noble member of the same family (right).