COLOGNE, GERMANY ? Thousands of cheering and singing young people from dozens of nations gathered in Cologne Tuesday, inaugurating World Youth Day with a jubilant Mass led by the city’s archbishop.

German-born Pope Benedict XVI will join the six-day Roman Catholic youth festival on Thursday in his first foreign trip. His predecessor John Paul II, the founder of the 20-year-old event and a favorite with young people, was still very much on people’s minds.

“The 20th World Youth Day is the first one with two popes,” said Cologne’s Archbishop, Joachim Meisner.

More than 400,000 people have registered for the World Youth Day, and organizers say as many as a million may turn up by the time the festival ends on Sunday.

The head of Germany’s Bishops Conference, Cardinal Karl Lehmann, urged the young Catholics to proudly display their faith in public, and many apparently took note of the advice.

Young people filed into Cologne’s gothic cathedral to pray, then poured into the city’s streets, dancing and singing religious songs. The festivities continued into the buildings housing them over the next few days, including a Turkish Islamic cultural center.