for pilgrims to see the dead pontiff, and occurs within a nine-day period of mourning known as the , . The congregations also fix the date and time of the commencement of the conclave. The conclave normally takes place fifteen days after the death of the pope, but the congregations may extend the period to a maximum of twenty days in order to permit other cardinals to arrive in the Vatican City. Resignation of a pope A vacancy in the papal office may also result from a papal resignation. Until the resignation of Benedict XVI on 28 February 2013, no pope had abdicated since Gregory XII in 1415. In 1996 Pope John Paul II, in his apostolic constitution Universi Dominici gregis, anticipated the possibility of resignation when he specified that the procedures he set out in that document should be observed "even if the vacancy of the Apostolic See should occur as a result of the resignation of the Supreme Pontiff". In the case of a papal resignation, the Ring of the Fisherman is placed in the custody of the Cardinal Camerlengo; in the presence of the College of Cardinals, the Cardinal Camerlengo marks an X (for the cross) with a small silver hammer and chisel into the ring, disfiguring it so it may no longer be used for signing and sealing official papal documents. In his book, Light of the World: The Pope, the Church and the Signs of the Times, Benedict XVI espoused the idea of abdication on health grounds, which already had some theological respectability. Before the sealing of the Sistine Chapel The cardinals hear two sermons before the election: one before actually entering the conclave, and one once they are settled in the Sistine Chapel. In both cases, the sermons are meant to lay out the current state of the Church, and to suggest the qualities necessary for a pope to possess in that specific time. The first preacher in the 2005 conclave was Fr. Raniero Cantalamessa, the preacher of the papal household and a member of the Capuchin Franciscan order, who spoke at one of the meetings of the cardinals held before the actual day when the conclave began. Cardinal Tomáš Špidlík, a former professor at the Pontifical Oriental Institute and a non-voting member (due to age) of the College of Cardinals, spoke just before the doors were finally closed for the conclave. On the