VATICAN CITY (AP) — Pope Francis celebrated Mass in St. Peter’s Basilica to mark Holy Thursday, hours before he was at an Italian prison to perform a foot-washing ritual for a dozen inmates in a gesture of humility.

Attending the Mass were some 1,800 priests. Francis in his homily advised priests not to focus on worldly concerns such as power, planning and bureaucracy. He exhorted them to “serve, with a clear conscience, the holy and faithful people of God.”

In the afternoon, the 85-year-old Francis was at a prison in Civitavecchia, a port town 50 milesnorthwest of Rome, for the foot-washing ceremony which recalls Jesus’ gesture of humility for his apostles.

Francis has made paying attention to those on society’s margins — including refugees, migrants and people in prisons — a hallmark of his papacy. On Holy Thursday in past years, he has gone to prisons in or near Rome.

This year finds him struggling with mobility issues. Francis suffers pain from a knee ligament problem and for years has been plagued by sciatica, a nerve inflammation affecting the legs and back.

During the Holy Thursday Mass, large urns of oil are blessed for use in ceremonies in churches in the Rome area. When Francis went to bless the oil by breathing into it, an aide helped him rise from his chair and walk toward the silver urn. At the end of the ceremony, Francis descended the steps down from the altar clinging to an aide’s arm, and even while assisted limped his way out of the basilica.

Holy Week, which draws hundreds of thousands of faithful to the Vatican, began with Palm Sunday Mass on April 10 in St. Peter’s Square.

Holy Week culminates on Easter Sunday.