VATICAN CITY — A simple marble slab was placed Saturday in St. Peter's Square on the spot where the late Pope John Paul II was shot in an assassination attempt 25 years ago.

The stone, which was quickly covered with flowers from the faithful, has been placed to help people "remember from now on that dramatic event," John Paul's successor, Pope Benedict XVI, announced in a message read to thousands of faithful during a Mass in St. Peter's Basilica.

Set flat into the square replacing cobblestones, the white stone bears the date in Roman numerals of May 13, 1981, when a Turkish gunman gravely wounded John Paul.

"Twenty-five years ago, our beloved Pope John Paul II shed his blood," said Rome Cardinal Camillo Ruini, who celebrated the Mass at St. Peter's.

"May he be soon beatified," the cardinal added, drawing applause. Beatification is the last formal step before possible sainthood.

Participants also honored the Madonna of Fatima, whose feast day is celebrated on May 13, the date in 1917 when three shepherd children in Fatima, Portugal, said the Virgin Mary appeared to them.