Vatican City ? He was the first pontiff in modern times to celebrate Palm Sunday Mass outside of Rome. Now, for the first time in his groundbreaking papacy, an ailing Pope John Paul II may himself be a spectator as throngs of faithful jam St. Peter’s Square to usher in Holy Week.

Potted olive trees surrounded the obelisk at the center of the square and row after row of gray plastic chairs were lined up in the vast space in preparation for today’s midmorning Mass, which commemorates Christ’s triumphant entry into Jerusalem.

But in a sign of the extent to which his health has deteriorated, John Paul won’t be presiding over one of his favorite ceremonies, which marks the start of the most important week in the Roman Catholic liturgical year. The week culminates with Easter on March 27.

The pope designated Cardinal Camillo Ruini, his vicar for Rome, to lead Palm Sunday Mass.

The Vatican said Friday that John Paul was expected to appear at his studio window on Palm Sunday. But it wasn’t clear if he might speak to pilgrims and tourists in the Square.

Accepting the advice of his doctors, John Paul’s only Holy Week commitment is an Easter Sunday blessing, while he regains strength at the Vatican after being hospitalized twice in a month with breathing problems. He was released from the hospital a week ago.

“I think the faithful are going to be very disappointed but there is nothing they can do. It’s life, even if it’s sad not to see him on a very special week for the Church,” said Gordon Bland, a 79-year-old retiree from London who was in St. Peter’s Square with his wife on Saturday.

Twenty years ago, John Paul started dedicating Palm Sunday to young people, whom he cherishes as the future of the Church.

In 1987 he became the first modern pontiff to celebrate the day outside of Rome when he led nearly 1 million people at the ceremony from an altar atop a three-story-high platform down the middle of a boulevard in Buenos Aires.