Harley Davidson riders took over the Vatican on Sunday as Pope Francis blessed thousands of them celebrating the 110th anniversary of the bike manufacturer.

The roar of engines nearly drowned out the traditional recitation of the "Our Father" prayer as the main street leading to St Peter's Square was turned into a giant parking lot.

On Saturday riders took part in a procession past the Colosseum. Some estimates say nearly half a million bikers had turned up for the event.

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  • Harley-Davidson motorcycles are parked in Via della Conciliazione leading to St. Peter's Square during a Mass celebrated by Pope Francis, at the Vatican, Sunday, June 16, 2013. Pope Francis on Sunday blessed thousands of Harley Davidsons and their riders as the American motorcycle manufacturer celebrated its 110th anniversary with a loud parade and plenty of leather. (AP Photo/Riccardo De Luca)

  • Pope Francis

    Pope Francis kisses a child as he arrives for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis

    Pope Francis spreads incense towards a statue of the Virgin Mary and child during a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis

    Pope Francis waves to faithful as he arrives for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis

    Pope Francis waves to faithful as he arrives for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis

    Pope Francis, center, celebrates a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis

    Pope Francis waves to faithful as he arrives for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis

    Pope Francis greets faithful as he arrives for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis

    Security guards surround Pope Francis as he waves to faithful upon his arrival for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013.(AP Photo/Riccardo De Luca)

  • Pope Francis

    Pope Francis waves to faithful as he arrives for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis

    Pope Francis waves to faithful as he arrives for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis

    Faithful reach out to Pope Francis as he arrives for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis

    A child is handed towards Pope Francis as he arrives for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Pope Francis waves to faithful as he arrives for a Mass in St. Peter's Square at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Riccardo De Luca)

  • Harley Davidson motorcycles riders park their motorcycles in Via della Conciliazione leading to the Vatican, seen at top, as they wait for Pope Francis to drive by to bless them ahead of mass in St. Peter's Square, at the Vatican, Sunday, June 16, 2013. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Andrew Medichini)

  • Pope Francis, figure in green under the canopy, celebrates a mass in St. Peter's Square, at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Andrew Medichini)

  • Harley Davidson motorcycles riders park their motorcycles in Via della Conciliazione leading to the Vatican, seen at left, as they wait for Pope Francis to drive by to bless them ahead of mass in St. Peter's Square, at the Vatican, Sunday, June 16, 2013. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Andrew Medichini)

  • Pope Francis celebrate mass in St. Peter's Square, at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Andrew Medichini)

  • Pope Francis arrives to celebrate mass in St. Peter's Square, at the Vatican, Sunday, June 16, 2013. The pontiff greeted hundreds of Harley Davidson riders and blessed their motorcycles prior to the start of the mass. The riders are gathered in Rome for a four-day event to celebrate the motorcycle company's 110th anniversary. (AP Photo/Andrew Medichini)

  • Harley Davidson motorcycles are parked as Pope Francis, white figure seen above the crowd at top right, arrives to celebrate mass in St. Peter's Square, at the Vatican, Sunday, June 16, 2013. Thousands of Harley-Davidson lovers have met in Rome to celebrate the motorcycle company's 110th anniversary. The four-day event includes a major parade through the heart of the city and a blessing by Pope Francis during his Angelus noon prayer at the Vatican on Sunday. (AP Photo/Andrew Medichini)

  • Harley Davidson motorcycles are parked as Pope Francis, top, arrives to celebrate mass in St. Peter's Square, at the Vatican, Sunday, June 16, 2013. Thousands of Harley-Davidson lovers have met in Rome to celebrate the motorcycle company's 110th anniversary. The four-day event includes a major parade through the heart of the city and a blessing by Pope Francis during his Angelus noon prayer at the Vatican on Sunday. (AP Photo/Andrew Medichini)

  • Harley Davidson motorcycles are parked as Pope Francis, top, arrives to celebrate mass in St. Peter's Square, at the Vatican, Sunday, June 16, 2013. Thousands of Harley-Davidson lovers have met in Rome to celebrate the motorcycle company's 110th anniversary. The four-day event includes a major parade through the heart of the city and a blessing by Pope Francis during his Angelus noon prayer at the Vatican on Sunday. (AP Photo/Andrew Medichini)

  • In this photo provided by the Vatican paper L'Osservatore Romano, Pope Francis meets with the President of the European Commission José Manuel Barroso during a private audience at the Vatican Saturday, June 15, 2013. (AP Photo/L'Osservatore Romano, ho)

  • In this photo provided by the Vatican paper L'Osservatore Romano, Pope Francis exchange gifts with the President of the European Commission José Manuel Barroso during a private audience at the Vatican Saturday, June 15, 2013. (AP Photo/L'Osservatore Romano)

  • Harley Davidson motorcycles parade through the center of Rome, Saturday, June 15, 2013. Thousands of of Harley-Davidson lovers are meeting in Rome to celebrate the motorcycle company's 110th anniversary. The four-day event includes a major parade through the heart of the city and a blessing by Pope Francis during his Angelus noon prayer at the Vatican on Sunday. In background is Rome's Colosseum. (AP Photo/Andrew Medichini)

  • In this photo provided by the Vatican paper L'Osservatore Romano, Pope Francis meets with the President of the European Commission José Manuel Barroso during a private audience at the Vatican Saturday, June 15, 2013. (AP Photo/L'Osservatore Romano, ho)