Although the parade didn't start for hours, people had gathered on downtown sidewalks by 7:15 a.m., The Baltimore Sun reported.
Tera Houser, 34, arrived for the parade after she and her husband had driven 18 hours overnight from New Orleans, where they attended the game.
The city should have canceled school for the day, some students said.
"With everything going on in the city today and all the traffic, schools should have been let out," said Joshua Green, 14. "It's not fair, because it's the city team. It should be a city parade, our parade."
The parade ended at the 71,000-seat M&T Bank Stadium, which was so packed that thousands of fans were forced by police to remain outside.
"When you wish upon a star" played as quarterback Joe Flacco was introduced.
"This is awesome,' he said, carrying his son to the microphone.
"I said this is my last ride, and every moment every time I've stepped into this stadium, what I've received is pure love," said Lewis, for whom the Super Bowl was his last game before retirement.
Coach John Harbaugh lauded the fans' determination to get to the stadium.
"We played with incredible determination and resolve," Harbaugh said, "and judging by how hard it was to get to this stadium, I would say that was true by our fans."
The last time the team won the Super Bowl, in 2001, about 200,000 gathered to celebrate.