Pope Benedict XVI (37 images)

Pope Benedict XVI holds a mass at Nationals Park in Washington on April 17, 2008. Approximately 50,000 people are expected in attendance for the Pope's mass. (UPI Photo/Kevin Dietsch)

Pope Benedict XVI acknowledges the crowd prior to delivering mass at Nationals Park in Washington on April 17, 2008. Approximately 50,000 people are expected in attendance for the Pope's mass. (UPI Photo/Kevin Dietsch)

Pope Benedict XVI is greeted by Donald W. Wuerl, Archbishop of Washington as mass is celebrated at Nationals Park in Washington on April 17, 2008. Approximately 50,000 people are expected in attendance for the Pope's mass. (UPI Photo/Roger L. Wollenberg)

Pope Benedict XVI celebrates mass at Nationals Park in Washington on April 17, 2008. Approximately 50,000 people are expected in attendance for the Pope's mass. (UPI Photo/Roger L. Wollenberg)