ROME Young people began to gather on a university campus south of Rome Saturday for World Youth Day, which is today will mark one of the centerpieces of the Roman Catholic church's holy year.
More than two million were expected to attend the event, called into life by Pope John Paul II in 1984.
It is also likely to pose massive logistical problems for organizers, who are particularly concerned about temperatures expected to reach well above 30 Celsius.
As many as 12,000 drinking fountains and 15,000 chemical toilets have been installed in the 300-hectare grounds of the Tor Vergata University. Organizers plan to distribute 10 million bottles of mineral water over the weekend.
The young people, dubbed "Pope's Boys" by the Italian media, will have to walk 10 kilometers to reach the grounds. They spent most of Saturday listening to concerts and praying ahead of a late vigil with the Pope.
Police said 500,000 had already reached the grounds by Saturday Morning. Authorities had to close down a nearby motorway to create enough parking space. Rome Mayor Francisco Rutelli appealed to Romans not to come back from their holidays before Monday, when the area will have been cleared.
Many of the youths plan to spend the night in tents ahead of Sunday morning's giant mass with the Pope.
Hundreds of thousands of youths from 160 countries on Friday walked along the way of the cross the largest such walk ever seen in Rome.
(DPA)