Pope Francis bowed his forehead to receive a dab of ashes, then smudged ashes in turn on the heads of other faithful during an Ash Wednesday service in an ancient Roman basilica.
Ash Wednesday begins the Catholic Church's annual Lenten period of reflection in preparation for Easter. The day's rituals include rubbing ashes on the head of faithful in a reminder of mortality.
Cloaked in purple vestments, Francis clutched his pastoral staff as he walked in a procession between two churches in the fading afternoon sun on the Aventine Hill.
He strode into St Sabina's Basilica, a 5th-century church that is considered among the most beautiful in Rome.
Lent is a time in which many faithful strive to go without something, like sweets or alcohol, or do more of something, like donate to charity.
In his homily, Francis suggested his own approach to Lent, which he described as "the time for saying no".
He urged faithful to swear off indifference, "harsh and hasty criticism" of others and "simplistic analyses that fail to grasp the complexity of problems, especially the problems of those who suffer the most".
He also advised faithful to "say no" to "prayer that soothes our conscience" as well as "almsgiving that leaves us self-satisfied."