VATICAN CITY – Pope Benedict XVI seems worn out.

People who have spent time with him recently say they found him weaker than they’d ever seen him, seemingly too tired to engage with what they were saying.

He no longer meets individually with visiting bishops. A few weeks ago he started using a moving platform to spare him the long walk down St. Peter’s Basilica.

Benedict turns 85 in the new year, so a slowdown is only natural. And given his age and continued rigorous work schedule, it’s remarkable he does as much as he does and is in such good health overall: Just this past week he confirmed he would travel to Mexico and Cuba next spring.

But a decline has been noted as Benedict prepares for next weekend’s Christmas celebrations, which kick off two weeks of intense public appearances. And that raises questions about the future of the papacy given that Benedict himself has said popes should resign if they can’t do the job.

Vatican spokesman the Rev. Federico Lombardi has said no medical condition prompted the decision to use the moving platform in St. Peter’s, and that it’s merely designed to spare the pontiff the fatigue of the 100-yard walk to and from the main altar.

And Benedict rallied during his three-day trip to Benin in west Africa last month, braving temperatures of 90 degrees and high humidity to deliver a strong message about the future of the Catholic Church in Africa.

Wiping sweat from his brow, he kissed babies who were handed up to him, delivered a tough speech on the need for Africa’s political leaders to clean up their acts, and visited one of the continent’s most important seminaries.

But back at home it seems the daily grind of being pope — the audiences with visiting heads of state, the weekly public catechism lessons, the sessions with visiting bishops — has taken its toll.

A spark is gone. He doesn’t elaborate off-the-cuff much anymore, and some days he just seems wiped out.

Take for example his recent visit to Assisi, where he traveled by train with dozens of religious leaders from around the world for a peace pilgrimage. For anyone participating it was a tough, long day; for the aging pope it was even more so.

That Benedict is tired would be perfectly normal for an 84-year-old, even someone with no known health ailments and a still-agile mind. He has acknowledged having suffered a hemorrhagic stroke in 1991 that temporarily affected his vision. His older brother, who has a pacemaker for an irregular heartbeat, has expressed concern about Benedict’s own heart.

Popes are allowed to resign; church law specifies only that the resignation be “freely made and properly manifested.”

Only a handful have done so, however. The last one was Pope Gregory XII, who stepped down in 1415 in a deal to end the Great Western Schism among competing papal claimants.

Yet Benedict himself raised the possibility of resigning if he were simply too old or sick to continue on, when he was interviewed for the book “Light of the World,” which was released in November 2010.