It was one of the most-watched and followed goodbyes of the world. Millions of TV viewers and thousands of visitors in Vatican City bade Pope Benedict XVI farewell on Thursday as the stepped down as leader of the Roman Catholic Church, which counts about 1.2 billion members.

He made modern papal history by being the first pope to resign in 600 years.

However, besides at least five pairs of red shoes and a growing number of sex abuse cases he left for his successor - who is yet to be elected - to handle, it appears Pope Emeritus left unfinished business behind.

Reuters reported that the ex-pontiff left an unfinished encyclical about faith. Vatican announced in 2012 that the pope was working on a new encyclical and expected to finish it by mid-2013. However, he made the unexpected decision of quitting.

In his eight-year term as the 265th pope, Pope Emeritus wrote three encyclicals that focused on social, economic and spiritual issues. These are God is Love in 2006, In Hope We Are Saved in 2007 and Love in Faith in 2009.

The fourth encyclical could have completed the virtues faith, hope and charity that the Catholic Church is espousing.

Before he boarded a helicopter, the pope met and said goodbye to the cardinals who are gathered in Vatican for the mid-March conclave.

The retired pope left aboard a helicopter on Thursday afternoon for several weeks of rest at Castel Gandolfo, the summer residences of pontiffs. Onlookers cheered and waved flags and brandished farewell placards, while church bells pealed to mark the final send-off for the 86-year-old man who was born Joseph Ratzinger in Germany.

His leaving is a radical departure from many of his predecessors who left Vatican on a journey, not for the papal summer residence, but inside a coffin to be buried. Some dead popes became saints. The popular Pope John Paul II, Pope Emeritus's predecessor was beatified a few months ago, the final step towards sainthood.

With his retirement, the shepherd of more than 1.2 billion Catholics is temporarily silenced as the retirement of Pope Benedict signaled also the closure of his Twitter account under the handle @Pontifex.

"Thank you for your love and support. May you always experience the joy that comes from putting Christ at the centre of your lives," was his final tweet on Thursday.

Techies are anticipating if the next pope would also tap social media to reach out to the faithful as the former pope did, although reports said that an aide was the one who actually typed the tweets using a dedicated computer in a secured location.

With Pope Benedict's retirement, all eyes are now on who will be the next pope, feared by some as an anti-Christ because of prophesies and association with the number 666 since the next pope is number 266.

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