An aerial view of St. Peter's Basilica is shown in this 2004 photo. A 450-year-old receipt has provided proof that Michelangelo kept a private room in St. Peter's Basilica while working as the pope's chief architect, Vatican experts said.

Vatican City ? A 450-year-old receipt has provided proof that Michelangelo kept a private room in St. Peter’s Basilica while working as the pope’s chief architect, Vatican experts said.

While going through the basilica archives for an exhibit on the 500th anniversary of the church last year, researchers came across an entry for a key to a chest “in the room in St. Peter’s where Master Michelangelo retires.”

The Renaissance painter and sculptor whose frescoes adorn the ceiling of the Sistine Chapel in the Vatican was put in charge of the restoration of St. Peter’s Basilica by Pope Paul III at age 71 in 1546, a job he held until his death in 1564.

Michelangelo’s greatest contribution to the basilica was his design for the central dome or cupola, a universally acknowledged architectural triumph.

“We now know that Michelangelo definitely had a private space in the basilica,” said Maria Cristina Carlo-Stella, who runs the Fabbrica di San Pietro, the office where the basilica’s archives are kept. “The next step is to identify it.”

Carlo-Stella spoke to The Associated Press in an interview in the past week.

The ink-scripted entry for the key was contained in a parchment-covered volume listing the expenditures of the Fabbrica for the years 1556-58. It refers to the payment of 10 scudos to the blacksmith who forged the key, but offers no details about the chest or the location of the room.

Vatican officials reported the find during the current exhibition, although the volume was not put on display.

The basilica – 610 feet long and 449 feet at its widest – took 120 years to build over a previous Roman basilica, constructed by the emperor Constantine. The first stone was placed by Pope Julius II in 1506, and Pope Urban VIII consecrated it in 1626.

A frescoed room with a fireplace in the area where the archives are housed has traditionally been called “la stanza di Michelangelo,” or Michelangelo’s room. Located on an upper floor in the left wing of the basilica, it is connected to the ground floor by a marble staircase.

However, research shows the room was added during renovations after Michelangelo’s death.

“The theory is very romantic and conspiratorial, but totally unfounded,” said Federico Bellini, an art historian who works in the archives department. He said a 16th-century sketch of the left wing of the basilica shows it was nothing more than a pile of rubble intertwined with vegetation during Michelangelo’s time at the Vatican.