The papal conclave from April 4-8, 1455 elected Alfons Borja Pope Callixtus III following the death of Pope Nicholas V. The conclave was the first in the Apostolic Palace, the site of all but five papal conclave thereafter. The conclave was also the first to feature accessus voting (votes cast in accessit), derived from a practice of the Roman Senate, where a cardinal could change their vote after an unsuccessful scrutiny to any cardinal already receiving votes.

More information, including a list of cardinals involved (15 out of the total of 21), on the Wikipedia page [1]

Community content is available under CC-BY-SA unless otherwise noted.