NEW : Vatican Secretary of State Tarcisio Bertone thanks Pope Benedict for his service . The pontiff will later celebrate an Ash Wednesday mass at Saint Peter 's Basilica . Much speculation has focused on whether Benedict 's successor might come from Africa or Latin America , rather than Europe , where Roman Catholic congregations are shrinking . Benedict cites age and frailty as the reasons for his surprise retirement . His successor as pope will be chosen at a meeting of cardinals in Rome .
NEW : Vatican Secretary of State Tarcisio Bertone thanks Pope Benedict for his service . The pontiff will later celebrate an Ash Wednesday mass at Saint Peter 's Basilica . Benedict cites age and frailty as the reasons for his surprise retirement . His successor as pope will be chosen at a meeting of cardinals in Rome .