There was a riot last time St Pierre's cathedral in Geneva hosted a Catholic Mass in 1535, with clergymen chased out and statues and treasures looted.
On Saturday, the first Catholic Mass since that day in what became a centre of the Protestant Reformation promises to be a more sedate affair.
Father Pascal Desthieux, who will celebrate the Mass, told AFP he planned to express "respect and gratitude" to Protestant friends for hosting it.
Desthieux said he would also apologise on behalf of all the Catholics who had "disrespected, misjudged and condemned" Protestants over the centuries.
The Reformation triumphed in Switzerland in 1536 under the leadership of John Calvin and the building -- which was run by the Roman Catholic Church for 1,000 years -- was taken over by the Protestant Church.
The cathedral, which has Calvin's wooden chair on display, "is a symbolic place for all Genevans", Desthieux said, adding that nearby Catholic churches would be closed to encourage the faithful to go there.
Pastor Emmanuel Fuchs, head of the Protestant Church in Geneva, said the 6:30 pm (1730 GMT) mass was a way of moving forward "on the path of reconciliation".
"We cannot remain prisoners of history. History has to elevate us, not keep us in a straitjacket," he said.
In a city where Catholicism is once again the main religion, Protestant and Catholic leaders said the two churches are already co-operating in many areas -- including joint chaplaincies for the sick or prisoners.
Even with widespread approval in both communities, however, Saturday's Mass remains a sensitive issue.
The Vatican and Protestant Churches still do not recognise each other's legitimacy and many Protestants remain highly suspicious of the papacy.
Religious leaders are careful to play down any suspicion that the Mass is an attempt by Catholics to regain lost territory in the land of Calvin.
"Some people are surprised, some disappointed, some may even be quite angry at this initiative," Fuchs said.
"But we are a Church that has a habit of debating, a church where we take decisions democratically. I think a large consensus has been achieved." Desthieux said there was "no hidden agenda" and "no intention to take back the cathedral".
"We already have our basilica and we have enough big churches," he said, referring to the Notre-Dame of Geneva basilica.
Fuchs said he was sure the Catholic Church would celebrate the Mass "with the intelligence and subtlety that the place and the moment demand".
Asked whether the experiment might be repeated, Fuchs said "let's see how things go" on both the Protestant and Catholic sides after the mass.
"We will have time to discuss it afterwards, to see what the fruit of this initiative could be," he said.
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