LONDON — When he became pope at age 78, Benedict XVI was the oldest pontiff elected in nearly 300 years. He is now 85, and in recent years he has slowed significantly, cutting back his foreign travel and limiting his audiences.

The pope travels to the altar in St. Peter’s Basilica on a moving platform to spare him the 100-yard walk down the aisle. Occasionally he uses a cane. Late last year, people who were spending time with the pontiff emerged saying they found him weak and too tired to engage with what they were saying.