For nearly 180 years, papal conclaves have chosen a new pope in three to five days. In centuries past, they've taken a lot longer.

When the cardinals meet for the conclave, they gather in the Sistine Chapel. All cardinal electors must swear an oath of secrecy and vote by secret ballot. A two-thirds majority is needed to elect a new pope, and campaigning is part of the process, though it should not appear so.

The Vatican’s cardinals’ assembly, known as the General Congregation, has chosen May 7 as the starting date for the highly secretive election that will choose the next pope, the Holy See said on Monday.