Originally it had two monumental Renaissance tombs facing each other, made for Cardinal Giovanni Battista Mellini and his brother, Pietro around 1478-83.

[1] The interior of the chapel is covered with a rich white and gold stucco decoration which also extends over the outer surface of the entrance arch.

The keystone of the arch is an escutcheon with crossed branches of lilies, a star and bread rolls (the traditional attributes of Saint Nicholas of Tolentino), flanked by two stucco half-figures holding garlands of fruit.

The young Saint Nicholas of Tolentino is dressed as an Augustinian friar in black habit, kneeling before an altar with hands clasped in prayer.

The Virgin has descended from heaven on a throne of clouds poised above the altar, and she is accompanied by a retinue of putti, one of them holding a branch of lilies, the traditional attribute of Saint Nicholas.

[3] The altarpiece is framed by a sumptuous gold and white stucco aedicule with fluted Corinthian columns and a segmented, broken pediment which is crowned by the symbol of the Holy Spirit, a shell with garlands of fruit and two putti.

The antependium of the altar is a modern stone slab with a bronze relief of Saint Francis and the Wolf of Gubbio made by Goffredo Verginelli.

The scenes are set in a richly detailed white and gold stucco frame and the eight panels are crowned with angel heads and ribbons.

Although they were brought to light, the paintings remain in a precarious state and many of the finer details and the original colours were irretrievably lost.

The scene where he distributes the blessed rolls, called Saint Nicholas' bread to the sick emphasizes his care for the ailing.

The female personifications can be identified by the usual attributes: Justice - scale and sword; Fortitude - lion, column, helmet, mace; Temperance - glass of wine, chalice (?

In case of The Allegory of Temperance the 18th-century layer was totally different, depicting an angel mixing water with wine and the personification holding a bridle.

The entrance of the chapel is barred by a marble balustrade with richly carved wooden doors that are decorated with the coat-of-arms of Cardinal Mellini (the letter M and diagonal stripes).

Giovanni Battista played an important part in the reconstruction of Saint Peter's Basilica during the reign of Pope Sixtus IV.

The sculpture shows a strong similarity to the figure of Raffaello della Rovere in the crypt of the Church of Santi Apostoli, Rome.

The relief of the slab shows the full-length image of the Bishop, surrounded by a frame of trefoil arch supported on slender twisted columns with the family coats-of-arms in the upper corners.

[6] The monument was erected by the cardinal's nephews, Mario and Urbano Mellini but only after a conspicuously long time their uncle's death.

The work was much admired in Algardi's day because it conveys a sense of Baroque piety combined with expressive realism and brilliantly observed, technically perfect details.

The monument itself is a classicising aedicule framed by flat pilasters with masks and crowned by a broken segmental pediment with the Mellini coat-of-arms in a conch.

The voluminous epitaph follows the stages of Giovanni Garzia's prestigious career from his youth until his death, including his important diplomatic missions for Pope Paul V to Philip III of Spain and the warring Habsburg brothers of Emperor Rudolf II and Matthias.

The monuments were attributed to Alessandro Algardi, and Wittkower claims that the bust of Mario "obviously echoes Bernini's Francisco I of Este and must date from after 1650".

The inscription says that Mellini was minister plenipotentiary at the Holy See of Maria Theresa, Empress and Queen of Hungary "in the most difficult times", and his tomb was erected by his nieces, Anna Serlupi and Giulia Falconieri and his nephew, Antonio Casali in 1760.