Under the soaring frescoes of Renaissance masters, 133 scarlet-robed cardinals gathered this afternoon inside the Sistine Chapel to select a new pope to lead 1.4 billion Roman Catholics around the world.

After more than three hours of intense seclusion, black smoke puffed out from the chapel’s chimney — signaling that the cardinals had not reached a decision during the first round of voting. Tens of thousands of people stood shoulder to shoulder in St. Peter’s Square to watch. When the smoke rose, many onlookers cheered; others groaned.

Our Rome bureau chief, Jason Horowitz, told us that black smoke had been widely expected on the opening day. “The first vote is generally symbolic, testing the strength of candidates,” he said. Here’s how the voting works.

The past two conclaves reached decisions within two days, but earlier votes have taken much longer. For now, the cardinals will retire to guest quarters at the Vatican — isolated during their deliberations, without phone or internet access and under oaths of total secrecy. They will vote tomorrow morning, and continue to cast ballots until a two-thirds majority agrees on a candidate.

Oddsmakers suggested that two top contenders are Cardinal Pietro Parolin of Italy, who was Pope Francis’ second-in-command, and Cardinal Luis Tagle of the Philippines, where the church is growing rapidly.

The election in many ways will turn on whether the cardinals want a pope who will follow Francis’ path of openness and inclusion or forge a different one. He appointed a vast majority of the voters.