The conclave to select the next pope has begun after Catholic cardinals from across the world filed into the Sistine Chapel Wednesday before sealing themselves inside.

Cardinals failed again Thursday morning to find a successor to Pope Francis, sending black smoke billowing up through the Sistine Chapel chimney after two more inconclusive rounds of conclave voting.

The Sistine Chapel, a sacred room in the Apostolic Palace in Vatican City, is one of the most famous chapels in the world—and this week, cardinals from around the world will gather inside to choose a new pope.