The Cappella Sistina (Sistine Chapel) is named after Pope Sixtus IV (r. 1471-84), who commissioned the Florentine architect Baccio Pontelli (1450-92) to rebuild the ancient Cappella Magna between 1477 and 1480.
The Sistine Chapel, which was consecrated on August 15th (Feast of the Assumption), 1483, is universally known for its frescoes by Michelangelo, Botticelli, Perugino and others. What is, perhaps, less well known is that since 1492 (apart from a few exceptions) the chapel has been the venue for the conclave, the meeting of the College of Cardinals convened to elect a new pope.
The cardinals must assemble in conclave, not sooner than 15 days, and not later than 20 days, after the pope's death. In theory the cardinals may vote for any adult male Catholic, but in practice every pope since 1389 has been a cardinal. Only cardinals under the age of eighty may vote in the conclave and a two-thirds majority plus one is required to elect a new pope.
There are normally two ballots in the morning and two in the afternoon, but on the first day of the conclave there is usually only a single ballot. The votes are counted and if the required majority has not been reached, the voting papers are burnt in a stove, which has been set up in the chapel with a chimney visible in St Peter's Square. A chemical is added to the voting papers, which turns the smoke black. This is a signal to the outside world that the vote has not produced a pope. However, if the vote has been successful, the chemical is omitted and the smoke is white, indicating that a new pope has been elected.