The last two frescoes painted by the Renaissance master Michelangelo are to be restored, the Vatican has said.
Some historians lobbied against the Sistine Chapel restoration
Michelangelo completed the giant The Conversion of Paul and The Crucifixion of St Peter in 1550, when he was 75.
Their restoration is part of a project to restore the Pauline Chapel - closed to the public - where they hang.
"We have already carried out a long period of preparation, and in the fall the works will begin," said the head of Vatican Museums.
The frescoes are of a muscular God extending a ray of light to Paul and of St Peter lashed to a crucifix under a stormy sky.
Water seepage, botched previous restorations and layers of grime will be gently removed during the process, expected to take four years.
Director general Francesco Buranelli told Reuters: "The two Michelangelo frescoes are the most important works, but there are other frescoes and a wealth of stucco work.
"Most of the work will be on the stucco."
Pope Paul III commissioned the building of the Pauline Chapel in 1537 for use as a private chapel.
It lies between St Peter's Basilica and the Sistine Chapel and now houses saints' relics .
Experts spent 14 years restoring the Michelangelo frescoes in the Sistine Chapel until they were stripped back to their original brilliant hues.
But some art historians and critics lobbied against the work, which they say alters the masterpieces' appearance.