Pope Benedict XVI has cancelled a visit to a prestigious university in Rome where lecturers and students have protested against his views on Galileo.
Anti-Pope slogans have appeared at La Sapienza
The Pope had been set to make a speech at La Sapienza University on Thursday.
Sixty-seven academics had said the Pope condoned the 1633 trial and conviction of the astronomer Galileo for heresy.
The Vatican insists the Pope is not "anti-science" - but in light of the protests they have decided it would be better for him not to attend.
Galileo had argued that the Earth revolved around the Sun.
The Vatican says the Pope will now send his speech to La Sapienza, instead of delivering it in person.
Pope Benedict was in charge of Roman Catholic doctrine in 1990 when, as Cardinal Ratzinger, he commented on the 17th-Century Galileo trial.
In the speech, he quoted Austrian-born philosopher Paul Feyerabend as saying the Church's verdict against Galileo had been "rational and just".
Galileo's inquisitors maintained the scriptures indicated the Earth was stationary.
An old controversy has come back to haunt the Pope
Galileo, a devout Catholic, was forced to renounce his findings publicly.
In 1992, Pope John Paul II expressed regret at the way Galileo had been treated.
"The error of the theologians of the time, when they maintained the centrality of the Earth, was to think that our understanding of the physical world's structure was, in some way, imposed by the literal sense of Sacred Scripture," he said.
The academics at La Sapienza signed a letter saying Pope Benedict's views on Galileo "offend and humiliate us".
They said it would be inappropriate for the Pope to open their academic year on Thursday.
"In the name of the secular nature of science we hope this incongruous event can be cancelled," said the letter addressed to the university's rector, Renato Guarini.
In a separate initiative, students at La Sapienza organised four days of protest this week. The first revolved around an anti-clerical meal of bread, pork and wine, the BBC's Christian Fraser reports from Rome.
The banner at their lunch read: "Knowledge needs neither fathers nor priests".
Vatican Radio said the protest at La Sapienza had "a censorious tone".