Pope Benedict XVI  shocked Catholics around the world Monday with his announcement that he will resign on February 28, becoming the first leader of the church to step down in six centuries.

Citing advanced years and infirmity as his reasons, 85-year-old Benedict revealed his plans to a small gathering of cardinals at the Vatican, telling them that after examining his conscience “before God, 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.