Although there had been an earlier rehearsal for the military, using a Middleton lookalike, this was a rehearsal for the bride and groom.
William, 28, wore a charcoal grey suit and Middleton, 29, wore a black dress as they arrived in a chauffer-driven Range Rover at sunset. Best man Prince Harry, 26, and the maid of honor, Kate's sister Pippa Middleton, 27, arrived in a silver van. They were flanked by two motorcycle police officers.
It was their last rehearsal before Friday's wedding, according to multiple news reports.
The crowd of onlookers first knew something was brewing when 12 officers marched out of a side entrance of Westminster Abbey. They blocked off the street near the cathedral as the vehicles pulled up.
"Everything came to a halt," says Cindy Rockwell from Lake Oswego, Ore. "Then the crowd just surged forward. There were so many people that you could hardly even move; everyone was trying to see them."
William and Middleton were quickly ushered into a side entrance. "It was really surreal," says Carolyn Houghton from Medford, Ore. "In America, the crowd would have been screaming. But here, everyone was very quiet and orderly. But I do wish they would have stopped and waved for a minute."
The couple remained in the cathedral for about 90 minutes, where they practiced the ceremony. Then they left - William returning home, and Middleton heading to her $8,000-a-night royal suite on the top floor of the Goring Hotel.