Thousands of demonstrators have protested in Istanbul ahead of Pope Benedict XVI's visit to Turkey. About 35,000 protesters were monitored by 4,000 police backed by armored vehicles.
The pope later said he did not share the view of the Byzantine emperor he quoted and issued an apology.
Youths wearing headbands with Islamic scripts, beating drums and waving Turkish flags chanted "the Pope made a mistake, our patience has run out" during the demonstration on Sunday.
The protest had been organised by pro-Islamic political party Felicity, whose leaders have said they were offended by the pope's comments.
The party also draped banners over welcome signs along the route from Istanbul's airport reading: "No to an alliance of crusaders, let the pope not come."
Police said they were preparing for many thousands people to attend the demonstration, the largest anti-pope protest to date.
Such protests have to be approved by the Turkish police, though spontaneous gatherings are not uncommon.
The pope said at the Vatican on Sunday: "Starting right now, I want to send a cordial greeting to the dear Turkish people, rich in history and culture."
A visit to Istanbul's Sultanahmet, or Blue Mosque, has been added to the pope's itinerary, a move seen as a further attempt at reconciliation with the Muslim world.
The pope has previously spoken out against Turkey's bid to join the EU, and has called for a return to fundamental Christian values in Europe.
His trip to Turkey will be his first official visit as pope to a predominantly Muslim country.
Turkey's ruling AK party has kept a low profile in preparations for this visit, with talks still in progress as to whether Tayyip Erdogan, Turkey's prime minister, will meet the pope.
With a general election due next year the AK party, which has roots in political Islam, must balance a rise in nationalism with their support base among conservative Muslims.
Benedict is scheduled to stay for four days and will meet the Istanbul-based leader of the world's 300 million Orthodox Christians, Patriarch Bartholomew I.