"Especially for people who have got used coming here for the audience and for the (Sunday) Angelus, it's something to be missed," he said.
Those lucky enough to have tickets for the final audience listened from seats in front of St. Peter's Basilica. Among them were many of the Roman Catholic Church's senior clergy. Others packed around the edges of the square and surrounding side streets, hoping to catch a glimpse of the pontiff.
Among the crowds were groups of pilgrims who had traveled to Rome for the special occasion, as well as local residents and curious visitors keen to share in the moment.
Benedict arrived and left in his Popemobile, allowing him to pass close by many people in St. Peter's Square.
Standing in the glass-topped vehicle, flanked by security, he waved as he slowly made his way along pathways through the crowds. Some waved flags and banners as they stood under cold but clear skies.
Normally in winter, the pope would give his weekly Wednesday general audience inside a hall within Vatican City, but the event was moved outside because of the anticipated huge crowds.
The pope didn't give the usual brief personal greetings to people afterward, but was to meet with delegations of heads of state in Vatican City.
Benedict, who stunned the world's Catholics when he announced his resignation just over two weeks ago, will leave office at 8 p.m. local time Thursday.
At that point, a transition period will begin, as around 115 cardinals gather in Rome to pick a successor in a secretive election known as a conclave.
The Vatican has been rewriting the rules to cope with an almost unprecedented situation -- Benedict is the first pope to resign in nearly 600 years.
He will meet with the cardinals Wednesday and Thursday, before being flown by helicopter to the papal summer residence at Castel Gandolfo.
There, from a balcony, he will greet crowds one last time before his resignation takes effect and the Swiss Guards, who by tradition protect the pope, ceremonially leave the residence's gate.
More details were given Tuesday of how the 85-year-old's life in retirement will play out.
He will keep the papal title Benedict XVI, rather than reverting to the name Joseph Ratzinger, and will be referred to as "his holiness," said the Rev. Federico Lombardi, a Vatican spokesman.
He will also go by the title his holiness "pontiff emeritus" or "pope emeritus."
Living out of the public eye in a small monastery within Vatican City, Benedict will wear a simple white robe, without the papal red cape, and will swap his red shoes for brown ones. He is expected to devote his time to prayer and study.
Catholic author Michael Walsh told CNN he was unsurprised by Benedict's desire for more privacy.
"He's a rather private man. He wants to get back to his books and his cats, he wants to get back to prayer," he said. "He's obviously coming towards the end of his life -- he's 85 -- so I understand that."