The figures between the triangles include two different types of figures – Old Testament prophets and pagan sibyls. Humanists of the Renaissance would have been familiar with the role of sibyls in the ancient world, who foretold the coming of a savior. For Christians of the sixteenth century, this pagan prophesy was interpreted as being fulfilled in the arrival of Christ on earth. Both prophets from the Old Testament and classical culture therefore prophesied the same coming Messiah and are depicted here. One of these sibyls, the Libyan Sibyl, is particularly notable for her sculpturesque form. She sits on a garment placed atop a seat and twists her body to close the book. Her weight is placed on her toes and she looks over her shoulder to below her, toward the direction of the altar in the chapel. Michelangelo has made the sibyl respond to the environment in which she was placed.
Julius II's decision to completely renovate the decoration of the Ceiling was probably due to the serious problems of a static nature that affected the Sistine Chapel from the earliest years of his pontificate (1503-1513). They must have been the result of the excavations carried out both to the north and to the south of the building for the construction of the Borgia Tower and for the new St Peter's. After a long crack had opened in the Ceiling in May 1504, Bramante, then the Palace architect, was charged with finding a solution and he fixed some tie rods in the area above the Chapel. However, the damage suffered by the old painting must have been such as to convince the pontiff to entrust Michelangelo with a new pictorial decoration. On 8 May 1508, the artist signed the contract which foresaw the painting of twelve apostles in the pendentives and ornamental motifs in the rest. Subsequently, at the request of Buonarotti himself, who considered the project to be a "poor thing", the Pope gave him a new commission in which he left the full planning of the programme to the artist. It is however quite likely that for his creation the artist availed of the cooperation of the theologians of the papal court. Michelangelo placed nine Central stories illustrating episodes of the Genesis within a powerful painted architecture, with at their sides figures of Nudes, holding medallions with texts taken from the Book of Kings. At the base of the architectural structure twelve Prophets and Sibyls seated on monumental thrones are countered lower down by Christ's forefathers, portrayed in the Spandrels and in the Lunettes ( north wall, south wall, entrance wall). Finally, in the four corner Pendentives , the artist illustrated some episodes of the miraculous salvation of the people of Israel. Michelangelo completed the first half of the Ceiling, that is from the entrance wall to the Creation of Eve, in August 1510. The work must have been completed by 31 October 1512, as the Pope celebrated Mass in the Chapel on 1 November.