Noto Cathedral reopened on Monday 11 years after the Sicilian Baroque gem's collapse sent the art world into shock.
"Today is a day of great celebration because one of the greatest churches Italian architecture has produced has been reopened," said Premier Romano Prodi at the inauguration of the UNESCO World Heritage Site.
"It seemed to have been lost. Instead today we have a celebration of reconstruction.
"It is absolutely splendid. More beautiful than can be imagined".
The cathedral dome caved in on the night of March 13-14 1996, after heavy rain seeped into cracks formed by a 1990 earthquake.
It took four years to clear away rubble and shore up the site, and another seven to bring it back to its former splendour.
Pope Benedict XVI thanked everyone who took part in the restoration of "the city of Noto's most important church, a real Sicilian Baroque masterpiece" in a letter read before its inaugural mass.
Salvatore Trincali, one of the Italian architects who planned the restoration, said that he felt like "the father of the bride" on Monday.
Restorers used materials as similar as possible to the ones that saw the great structure rise between 1703 and 1776 - in the wake of a catastrophic earthquake across southwest Sicily at the end of the 17th century.
Around 50 restorers worked daily since January 2000 to put nearly 6,000 ornate decorations back in place.
"Today is an important day for Italy because this splendid cathedral has finally reopened," said Monsignor Angelo Bagnasco, the head of the Italian bishops' conference.
"There has been great cooperation by everyone. This is a great success and a legitimate source of pride, not just for the people of Noto, but for all of us".
Making it a World Heritage Site in 2002, UNESCO said Noto and the seven other towns in its valley were "a testament to the exuberant genius of the art and architecture of the late Baroque".
Nestling between the provinces of Catania, Ragusa and Siracusa, the Val di Noto is a striking juxtaposition of rocky hills, Mediterranean vegetation, cultivated fields and some of the most beautiful churches and palaces in the European Baroque.
Italian high-brow film director Michelangelo Antonioni, once seen as the master in finding visual expression for human alienation, shot part of his 1960 film L'Avventura in Noto.
Salvatore Cuffaro, the president of the Regional Government, said the restored Noto Cathedral should "become a symbol of a Sicily that wants to rebuilt itself, starting with the monuments that have characterized its history".
Last week Texas-based Panther Eureka oil company dropped plans to drill wells in the Val di Noto, following fierce protests from local people and environmentalists led by Sicilian crime writer Andrea Camilleri.
