In fact, the finger had been considered irreparably lost. But in 2010 Aurélia Azéma, a French Ph.D. student researching welding techniques used in making ancient large bronzes, hypothesized that the Louvre digit might belong to the Constantine at the Capitoline. The theory was confirmed eight years later when a French team of scholars and a curator from the Louvre made a resin reproduction of the finger from a 3-D model and went to the Capitoline to see if it fit.
“It was perfect,” Ms. Azéma said in an email. “Like two pieces of a puzzle.”
Mr. Parisi Presicce said that at the time, Jean-Luc Martinez, president-director of the Musée du Louvre, “immediately decided it was right” for the finger to be returned to its hand, he said.
The finger had found its way to the Louvre in 1863, where for a brief time (1913-1915) it had been cataloged as a toe. It arrived via a large group of artworks that had once belonged to Giampietro Campana, a Roman art collector and archaeologist who had amassed one of the great collections of the 19th century.
He was accused of embezzlement in 1857, and his collection was confiscated and put up for sale in 1861. Napoleon III acquired one large lot, which was exhibited at the Louvre, and another lot was acquired by Emperor Alexander II for the Hermitage in St. Petersburg, Russia.
Finally, the Louvre finger arrived at the Capitoline this week for a “renewable loan,” the French museum said in a statement. It was affixed to the hand “though an almost invisible, noninvasive and reversible system,” Mr. Parisi Presicce said.
The newly rejoined hand is exhibited next to the other pieces that made up the original nucleus of statues donated to the public by Sixtus IV, which include the “She-wolf,” the famed symbol of Rome.