The Basilica is divided into three naves of which the greatest one reaches a height of 16 metres and has a ratio of two to one compared to the lateral ones. In the central nave the fresco over the altar represents the “Vision of S. Pious V “, while the side-chapels are dedicated to S. Antonio and Maria SS. Immacolata. The external walls are made in Pliocene sandstone and the pillars are in bricks and tiles mixed with mortar, while the grand coat of arms of Pious IX  is inserted inside a garland in the fastigium of the main external front. The central nave is covered by a barrel vault with lunettes and six arch-windows, interpolated by bundles which mark the sequence of the trusses.

The tiara and the fleur-de-lys seem the easiest symbols to read in the vast outline of framings charged with meaning, work done by the artist Carlo Oglietti. A svelte frame, animated by a series of dentils and ovoli, runs round the perimeter of the nave, over a twirled frieze and an architrave with fillets. Twenty-two Ionic-styled pilasters divide up the inside; in the plumes, which border of the arches, a mosaic of golden tesserae replaces the pictures of the Passion of Jesus.  

The painting is an academic work of the Roman purism school inspired by the Venetian use of vivid effects( red tinges everything, the cape, the shoes, the cushions, the book of prayers, the clothes of the Divine messenger with the fiery sword and the Cross on the sails) and by the Tuscan predominance of graphic elements (the perspective of the prie-Dieu, the Cross and the refined flooring). The pose of the Pope is the same as that of a priest preparing himself to give the final blessing while the aura of light represents the Divine sign. 

Saint Anthony preaching to the fishces  (The painting is not shown)

It is an oil-painting on canvas (275 x 180 centimetres) done in 1856 by Marcello Sozzi, a master of the Roman purism, disciple of Minardi. The principal character is noted even by the colour of his soutane which emphasises by contrast the chromatic delicacy of the work. The carrying lines of the composition turn one’s eyes to its edges; they fix the focal length nearly out-of-frame, and so the portrayal of the characters, caught in profile, is made easier and we too are projected inside the event.   It is a painting with talking hands par excellence: here the gestural expressiveness of those present reveals the mood of witnesses to a prodigious event. Brother Anthony is talking to the crowd which is not paying attention to his sermon and turning himself toward the sea, he says: “ If you do not want to listen to me, then fishes will ”; suddenly the fishes appear on the surface and the bystanders, struck by surprise, seem to guard the miraculous fact while, in the right, a group of  gloomy astounded heretics, ask each other about the event.