Donald Trump joins a list of presidents visiting the Vatican.
The first was Woodrow Wilson who, almost 100 years ago, visited Benedict XV in 1919, when the Vatican was not yet an independent state.
The next US president at the Vatican was Dwight D. Eisenhower, who met with John XXIII 40 years later.
John F. Kennedy, the only Catholic elected to the Oval Office, was greeted by Paul VI at the Vatican in 1963.
Pope Paul VI also met with President Lyndon B. Johnson in 1965. The meeting was held in New York's Waldorf Astoria.
John Paul II was the first pope to visit the White House, where he was welcomed by Jimmy Carter in 1979. Throughout his pontificate, he held 15 meetings with US presidents. Bill Clinton and both Bush's came to his funeral in Vatican City.
In 2008, Benedict XVI visited the White House on the day of his 81st birthday. There he listened to a beautiful 'Happy Birthday.'
'Your Holiness, thank you very much. It is a great honor for me.'
In July 2009, Barack Obama visited the Vatican for the first time. He returned five years later, in 2014, to meet Pope Francis.
A little over a year later, the Argentine pope returned the visit and met him in Washington. With almost 100 years of meetings between the US presidents and popes, the general consensus is that though they have not always agreed, good relations have been undoubtedly useful for both sides.