( AP ) - A long-missing Michelangelo sketch for the dome of St. Peter's Basilica, possibly his last design before his death, has been discovered in the basilica's offices, the Vatican newspaper said Thursday.
The sketch, drawn in blood-red chalk for stonecutters who were working on the construction of the basilica, was done by the Renaissance master in the spring of 1563, less than a year before his death, L'Osservatore Romano reported.
"The sureness in his stroke, the expert hand used to making decisions in front of unfinished stone, leave little doubt, the sketch is Michelangelo's," the newspaper wrote about the discovery, which it said will be presented at a news conference at the Vatican on Monday.
The sketch shows that Michelangelo "on the threshold of 90 years of age, even though he wasn't coming regularly to the (basilica) construction site, continued to take binding decisions" on how the work was being carried out, the Holy See's official newspaper commented.
The sketch "now becomes the last known design of the artist," the newspaper said.
Michelangelo, who began working on the basilica's construction in 1547, was in his late 80s when he did the sketch. The sketch is especially rare, the Vatican newspaper noted, because the artist ordered many of his designs destroyed when he was an old man.
The sketch was discovered in the Fabbrica of St. Peter's, which contains the basilica's offices.
L'Osservatore Roman said most sketches done by Michelangelo for the stonecutters were destroyed or lost in the cutters' workplaces, but this one survived because a supervisor used the back of the sketch to make notes about problems linked to the stone's transport through the outskirts of Rome.
Assistance in the research for the sketch came from the University of Bonn and Rome's Bibliotheca Hertziana.
Michelangelo apparently drew the sketch for the stonecutters because he was dissatisfied with how with some blocks of travertine were cut, the newspaper said.
Travertine is a particularly resistant stone still used today in building homes and offices in Rome.
Michelangelo's design shows a spur of the drum of the dome to indicate to the cutters just how much stone needed to be hewn. Included on the sketch were three numbers - "6, 9 and 3/4" - but it was not clear what the figures referred to.
Michelangelo completed the dome and four columns for its base before he died in February 1564. Three weeks before he died, when he was nearly 89, Michelangelo went up the dome to inspect it.
The construction of the basilica, whose cupola defines Rome's skyline, spanned several working lifetimes of some of the Renaissance's most celebrated artists and architects.
The first architect of the basilica, Donato Bramante, died eight years after the cornerstone was laid. Other architects, including Raphael, followed, until Pope Paul III turned to Michelangelo in 1546 - 32 years after the artist had put the last brush stroke on the Sistine Chapel's frescoed ceiling.