Symbols of Pope Benedict XVI's final hours

Pope Benedict XVI's final hours as pontiff on Thursday will be filled with tradition and symbols that underline the historic -- and novel -- nature of his resignation as leader of the Catholic Church.

Benedict will board a helicopter at around 1600 GMT to fly to the papal summer residence of Castel Gandolfo outside Rome, where he will stay until his powers formally expire at 1900 GMT.

Here are a few key facts about the day:

Bell: The ancient bell of the Senatorial Palace of the Capitol -- Rome city hall -- will ring out three times when Benedict leaves the Vatican for the last time as pope at 1600 GMT and again at 1900 GMT.

Last Tweet: One final tweet will appear on the 85-year-old pope's Twitter account @pontifex at 1600 GMT before it is suspended until a new pope decides whether he wants to be a microblogger too.

Last public remarks: Benedict will come out onto the balcony of Castel Gandolfo at around 1630 GMT to bid one last goodbye to local townspeople before he retreats from the public eye forever.

Swiss Guards: The Swiss Guards will close the doors of Castel Gandolfo and quit their posts at exactly 1900 GMT.

The guards -- a military corps which dates back to the 15th century -- will change from their colourful striped regalia into civilian clothes and return to Rome.

Seals: Also at 1900 GMT, Vatican staff will apply seals to the doors of the papal apartments in accordance with tradition, as well as to the private lift used to reach the apartments on the third floor of the Apostolic Palace.

Fisherman's Ring: Benedict will entrust his Fisherman's Ring -- a potent symbol of the papacy that is cast in gold for each new pope -- to the "camerlengo" (chamberlain) cardinal who takes over Church affairs until a new pope is elected.

In a tradition first established to prevent forgeries of papal documents during the interim period known as the Sede Vacante (Vacant See), the camerlengo will score the signet ring with an "X" at the cardinals' first meeting next week.