His resignation as pope in 2013 shocked the world.

ROME — When Benedict XVI resigned in 2013, he was the first pope to do so in six centuries, and the move sent shock waves around the world.

Benedict announced the decision in Latin during a routine gathering of cardinals, telling them that after much thought, “I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise” of leading the world’s one billion Roman Catholics.

He told the cardinals that, at age 85, he did not have the strength, either of mind or body, to “adequately fulfill the ministry entrusted to me.”

Benedict had been showing signs of age, often appeared tired and used a wheeled platform to move around.

His papacy had also been roiled by fresh revelations of clerical abuse of minors in various dioceses around the world, and Benedict had struggled to respond to growing criticism.

After Benedict’s resignation, he moved into the Mater Ecclesiae Monastery on the grounds of Vatican City, where he said he would devote his life to meditation and prayer. He was cared for by four laywomen who had taken vows in the Catholic movement known as Communion and Liberation, as well as by Archbishop Georg Gänswein, the German monsignor who was his private secretary throughout his pontificate.

With two living popes for the first time in the modern era, the Vatican was forced to navigate a series of unknowns, including where to house two popes at the Vatican and what to call Benedict. The decision was made for Benedict to adopt the title of “pope emeritus” and continue to wear white.

The previous pope to resign, Pope Gregory XII, stepped down in 1415, in an attempt to quell a leadership crisis in the church known as the Great Western Schism, during which three men vied to be pope.