In 1507 Julius II granted assent to the acquisition of a chapel in the church to his friend, the wealthy Sienese banker and financier of the Roman Curia, Agostino Chigi.

The bull also stated that the chapel was meant to be a mausoleum for Agostino and his heirs, "wishing to trade earthly things to heavenly and transitory to eternal by fortunate exchange.

Agostino Chigi's widow, Francesca Ordeasca commissioned the mosaicist, Luigi da Pace on 31 May 1520 to create another set of mosaics for the planned decoration of the tambour and the spandrels, but she died in the same year on 11 November.

Vasari records in his Lives, speaking about the statues of Jonah and Elijah: "... the heirs of Agostino, with scant respect, allowed these figures to remain in Lorenzetto's workshop where they stood for many years.

Bernini finished the pyramids, laid the present floor, raised the altar, slightly enlarged the windows, renewed the lead roof, regilded and cleaned the dome.

The exterior is practically invisible due to the location of the chapel behind the city wall, the Porta del Popolo and the main body of the basilica.

The simple cube is surmounted by a hemispherical dome resting on a high drum which is penetrated by a row of windows that allow light into the chapel.

The trapezoidal pendentives were the characteristics of Bramante but the whole conception of space, which requires the viewer to look at from several points of view to capture its splendor, is new and unique.

The central roundel represents God, the Father, surrounded by putti, effectively foreshortened in an impetuous gesture, harking back to Michelangelo, which seems to give rise to the entire motion of the universe below.

Eight mosaic panels show the Sun, the Moon, the starry sky and the six known planets as pagan deities depicted in half-length, each accompanied by an angel with colourful feathered wings.

The portrayal of Ver (Spring), Aestas (Summer) and Autumnus (Autumn) follows Ovid's description of the seasons in his Metamorphoses (Met 2.27-30) while the allegory of winter was inspired by the "February-by-the-fire" motif of medieval calendar tradition.

[12] Due to their location and bad visibility the Salviati frescos have always been somewhat overlooked but the copies sent for the Duke of Lerma prove that they were held in high esteem at the time.

The scenes require the viewer to move his gaze along the wall of the drum, and it is only at the end of this visual journey that he has reconstructed the story in its entirety", claims Florian Métral.

[13] The windows also play their part in the overall effect because the sunlight breaks through each of the bays in turn, illuminating certain scenes and making others indiscernible, thus modulating the viewer's visual experience over time.

Looking at the whole cycle the scenes are gradually getting darker as the narrative progresses, except the oddly positioned Creation of the Animals which belongs to the first group of paintings regarding its treatment of light.

Vasari gives a scathing account in his Lives: "He did little work there, although we find that he obtained from the liberality of Agostino and his heirs much more than would have been due to him even if he had finished it completely, which he did not do, either because he was weary of the labors of art, or because he was too much wrapped up in comforts and pleasures.

According to Costanza Barbieri the presence of God in the upper part combines the traditional subject of the nativity with the doctrine of the Immaculate Conception which was still not generally accepted but it was heavily promoted by Pope Sixtus IV, and by Agostini Chigi, who requested in his will the celebration of a solemn mass in his chapel on the day of the birth of the Virgin.

They are intently browsing voluminous codices turning to the right and the left, an appropriate visualization of the sapiential books; the same motif appears on a modello drawing by Sebastiano for an altar-piece depicting the Assumption in the Rijksmuseum.

Anyway it was placed on the only existing pyramid at the time, the tomb of Agostino Chigi, and later it was moved to the main altar by Bernini who set it into a luminous golden-yellow stone frame.

The first time when "sepulchres" are mentioned in plural form is in a contract between the Chigi family and Bernardino da Viterbo on 8 April 1522 when the sculptor was commissioned to add the final touches to Lorenzetto's work.

He interpreted the text as a proof that the pyramid of Agostino was originally planned for his wife, Francesca Ordeasca together with the bronze relief of Christ and the Samaritan woman.

[19] This theory remains disputed but the corrected text indeed speaks about a female tondo which had not been executed by Lorenzetto - a hint that the second pyramid was prepared for a woman, most probably Ordeasca.

Another drawing, an architectural phantasy with the figures of Pyramus and Thisbe by Jean Lemaire (c. 1650) shows a similar pyramid obviously inspired by the one in the Chigi Chapel before it was restored by Bernini.

[21] The new medallions were made of white marble by an assistant sculptor from Bernini's workshop, and instead of the planned copper plates the funerary inscriptions are composed of freestanding bronze letters.

The clue to their real meaning was given by a well-informed contemporary description which remained unpublished: Benedetto Mellini's Saggio della Roma Descritta which was written around 1656.

The lunette paintings thematically complement Sebastiano del Piombo's altar-piece creating a link between the nativity of the Virgin and the stories of the Old Testament depicted on the tambour.

In his diary the Pope confirmed the great sculptor's authorship: "Yesterday, we saw the bronze lamp made for the chapel in the Popolo by Bernini", he wrote on 16 July 1657.

A drawing by a follower of Bernini in the Royal Collection, dated between 1655 and 1665, shows a design for a similar object, although the sketch might have been created for the altar candles of Saint Peter's Basilica.

They were supplemented by gilded wooden altar cards and a bronze crucifix-tabernacle, the chest of which was supported by four seraphim and the door decorated with a chalice and a radiant host.

"As a painter Raphael was naturally attracted to the vivid colours of the different kinds of stones available in Rome since the antiquity, and his patron, Agostino Chigi was one of the few people rich enough to finance a project that aimed to recreate the largely lost chromatic exuberance of ancient architecture.