Alessandro Petacchi of Italy, ahead of the pack that crashed, won the stage and immediately blamed Tour organizers for the pileup, saying the corner where the accident took place was dangerous.
The crash was caused by a rider who slipped going into the final turn at Meaux, east of Paris. Other riders behind, cycling virtually flat-out, piled into him. They included Armstrong, who is vying for a record-tying fifth consecutive title.
Several riders were injured. U.S. rider Tyler Hamilton, a former teammate of Armstrong's now cycling for the CSC team, was taken to a hospital for X-rays, the team said.
Armstrong completed the race on the bike of his U.S. Postal teammate, Jose Luis Rubiera. Armstrong had a flat, and the wheel wasn't able to turn, so Rubiera got off his bike and handed it to Armstrong.
The 31-year-old Texan held his hand to his back as he later boarded the team bus, but he had no outward injuries.
``I don't know who else was involved, but that was one hell of a crash,'' Armstrong said. ``It is never good to crash, but it wasn't that bad. We all just fell over and got piled on top of.''
``It kind of makes for a hard day but it's good to get the first one over with. Unfortunately, we had a bad ending at the end of it, but it's OK.''
Two of his U.S. Postal teammates also went down. George Hincapie suffered cuts on his left knee, and Vjatceslav Ekimov suffered scratches, said team spokesman Jogi Muller. Muller said Armstrong bruised his right thigh and scratched his left shoulder.
Before the race, Armstrong said his goal for the day was to stay out of trouble and save his strength for a team time-trial later in the week and mountain stages, where he often leaves rivals in his wake.
``It's a dangerous week, as we all know, and you need to avoid problems and accidents,'' he said.
Petacchi beat out Robbie McEwen of Australia in the dash for the finish line. German Erik Zabel was third.
The race started from Le Reveil Matin, a restaurant in the southeastern Paris suburb of Montgeron. The first Tour started there in 1903. Today, the restaurant serves French cuisine and Tex-Mex.
From there, the riders first cycled south before turning east and then north to finish in Meaux, a town of 50,000 people known for its Brie cheese and mustard. Meaux is about 40 kilometers (25 miles) east of Paris. The Tour has never stopped here before.
The 168-kilometer (104-mile) route took the riders past ripened fields of golden wheat, the lush green forest of Fontainebleau and through picturesque villages. Waving fans along the route cheered the riders on.
Before the race, the riders first gathered at the Stade de France, the stadium in northern Paris that hosted the 1998 soccer World Cup final, and paraded from there through Paris to the start at Montgeron.
On Monday, the Tour's third day, the riders cover 204.5 kilometers (126.8 miles), skirting Champagne country and the cathedral town of Reims, where French kings were crowned. They finish in Sedan, a town on the border with Belgium where German troops broke through during their invasion of France in 1940.
Stage 1 results, top 15 (Montgeron - Meaux, 168 km)
1. Alessandro Petacchi, Italy, Fassa Bortolo, 3 hours, 44 minutes, 33 seconds.
2. Robbie McEwen, Australia, Lotto-Domo, same time.
3. Erik Zabel, Germany, Team Telekom, same time.
4. Paolo Bettini, Italy, Quick Step-Davitamon, same time.
5. Baden Cooke, Australia, fdjeux.com, same time.
6. Thor Hushovd, Norway, Credit Agricole, same time.
7. Oscar Freire, Spain, Rabobank, same time.
8. Luca Paolini, Italy, Quick Step-Davitamon, same time.
9. Romans Vainsteins, Latvia, Caldirola-So.Di, same time.
10. Jaan Kirsipuu, Estonia, AG2R Prevoyance, same time.
11. Rene Haselbacher, Austria, Gerolsteiner, same time.
12. Damien Nazon, France, Brioches La Boulangere, same time.
13. Stuart O'grady, Australia, Credit Agricole, same time.
14. Jean-Patrick Nazon, France, Jean Delatour, same time.
15. Gerrit Glomser, Austria, Saeco-Macchine Per Caffe, same time.
27. Jan Ullrich, Germany, Bianchi, same time.
39. Iban Mayo, Spain, Euskaltel, same time.
65. David Millar, Cofidis, Cofidis-La Credit Par Telephone, same time.
69. Bradley McGee, Australia, fdjeux.com, same time.
83. Tyler Hamilton, United States, Team CSC, same time.
107. Lance Armstrong, United States, U.S. Postal Service, same time.
96. Fred Rodriguez, United States, Caldirola-So.Di, same time.
144. George Hincapie, United States, U.S. Postal Service, same time.
183. Levi Leipheimer, United States, Rabobank, same time.
189. Floyd Landis, United States, U.S. Postal Service, same time.
Stage 1, overall standings
1. McGee, 3:51.55.
2. Millar, 4 seconds.
3. Haimar Zubeldia, Spain, Euskaltel-Euskadi, 6 seconds.
4. Ullrich, 6 seconds.
6. Victor Hugo Pena, Colombia, U.S. Postal Service, 10 seconds.
7. Andy Flickinger, France, AG2R Prevoyance, 10 seconds.
8. Armstrong, 11 seconds.
9. Joseba Beloki, Spain, Once-Eroski, 13 seconds.
10. Santiago Botero, Colombia, Team Telekom, 13 seconds.
11. Vjatceslav Ekimov, Russia, U.S. Postal Service, 15 seconds.
12. Michael Rich, Germany, Gerolsteiner, 15 seconds.
13. Leipheimer, 15 seconds.
14. Hincapie, 15 seconds.
15. Vladimir Karpets, Russia, ibanesto.com, 16 seconds.