The imagery produced in the vault of the staircase is indicative of the cultural interests of the patrons of the building, Alessandro Vitelli and Angela Paola dei Rossi of San Secondo. The decoration was commissioned in the 1540s to Nicola Filotesio, known as Cola dell’Amatrice (1470/75-post 1547). The artist was summoned directly by Alessandro Vitelli who in 1538 received the fief of Amatrice from Carlo V.
The vault is divided in a decorative layout that includes the representation of Apollo e le Muse in the central axis, and tales of the god in the lateral panels. In the centre, there is the medallion with the coat of arms of Alessandro Vitelli, the chessboard with the half moon and the lying down calf, and that of Angela Rossi, the rampant lion. In the upper oval shape, Apollo is portrayed as a Prince to the muses: in one hand he has a lyre and in the other a bow and arrow, whilst at his feet his qualities can be recognised, an archery quiver, a three-headed dragon, and a raven. In the lower medallion a muse identified as Clio is depicted, muse of history, maybe in a prominent position because of her attribute of the swan, one of the symbols of the Rossi family. To the sides, the other eight muses are posed on a blue background, recognisable from the top to the bottom and from left to right: Calliope, muse of the elegy with a wax tablet and trumpet, Urania, muse of astronomy e astrology with an armillary sphere and a compass, Tersicore, muse of choral opera and dance with a guitar, Erato, muse of amorous poetry with a headband of cymbals, Melpomene, muse of tragedy playing the horn, Polimnia, muse of sacred music holding an organ, Euterpe, muse of lyrical poetry with an aerophone and Talia, muse of comedy holding a lira da braccio, a stringed instrument played with a bow. In the depiction of the muses, the artist seems to have taken inspiration from the so-called Tarocchi del Mantegna, a group of fifty etchings published between 1460 and 1465.
At the peak of the vault is a painting which depicts two panting calves under an oak tree: according to some, this is an allusion to the battle between Pope Sisto IV della Rovere (the oak tree) and Niccolò Vitelli. The city siege on the side of the papal troops in 1474 was amongst his most tense events, and subsequently condemned Niccolò to exile, only ending when he came back to the city of the Vitelli family in 1482 after the signing of an agreement.
In the semicircle and trapezoidal panels situated to the sides, the stories of the god Apollo are depicted, derived from Metamorfosi by Ovidio. From bottom to top and from left to right you can see: a contest between Apollo and Marsia, Apollo flaying Marsia, Apollo and the Pitone snake, the punishment of Mida, a contest between Apollo and Pan, Apollo and Dafne.