Although the White House is more than 200 years old, just two Popes have ever stepped foot inside. When Pope Francis visits Washington, he'll become the third.
The first sitting U.S. President to meet a reigning Pope was Woodrow Wilson. He saw Pope Benedict XV at Vatican City in 1919. It wasn't until forty years later that another meeting like it would happen. In 1959, Pope John XXIII and President Dwight Eisenhower met.
However, the meetings have since become a tradition. Almost every president since Eisenhower has held multiple meetings with the leader of the Catholic Church.
John F. Kennedy, the only Catholic president, visited Pope Paul VI at Vatican City. Two years later, the same Pope became the first one to visit the United States. While there, he met with JFK's successor, Lyndon B. Johnson in New York.
Pope John Paul II revolutionized the relationship between the U.S. and the Vatican. Formal relations were established during the Reagan administration, and he had 15 meetings with Presidents.
The Polish pontiff was also the first one to visit the White House, when he met with President Jimmy Carter in 1979.
Pope Benedict XVI famously celebrated his birthday at the White House in 2008. He took in a classical music performance and was given a special cake by President George W. Bush.
Bush's successor, Barack Obama, has only met Pope Francis once. But he has spoken highly of him several times, and the two will deepen their relationship when they have an intimate meeting inside the Oval Office.