The delicate restoration project began in 2015. During the works, an inscription was discovered on the main group of figures proving that it was completed in 1486, three years earlier than previously thought.
Workers also found the inscription of a carpenter working at the altar in 1957 during a previous renovation project.
The altarpiece has undergone several restorations in its more than 500-year existence. It has also been caught up in Poland's turbulent history.
During the Nazi occupation of Kraków, the altarpiece was taken apart and shipped to Germany. It was discovered in 1946 in the basement of Nuremberg Castle. It was returned to Poland and carefully reassembled at the basilica following major renovation work.
St. Mary's Basilica is located in Kraków's Main Square and is famous for its daily trumpet call, which breaks off abruptly, reputedly in memory of a trumpeter who was shot in the throat while sounding the alarm ahead of an attack on the city.
The basilica is associated with St. John Paul II, who served as a confessor at the church before he was appointed an auxiliary bishop of Kraków.
"We still have a confessional in which Fr. Karol Wojtyła confessed," said Msgr. Raś.
"We use it for confession only on holidays. It is carefully respected and marked by us. We call him a silent witness to so many confessions of John Paul II."
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He added: "We invite everyone to St. Mary's Church as soon as the inconvenience caused by the pandemic is over. It is worth seeing this unique monument in the world."