Next year's Tour de France route will be dominated by mountain stages, race organisers revealed on Thursday.
London hosts the Tour's prologue for the first time
The 2007 race, which begins in London on 7 July, features six mountain stages instead of five and a tough summit finish on the Col de l'Aubisque.
Director Christian Prudhomme said: "For the first time in 20 years, the last mountain stage finishes at the summit.
"It will be the toughest stage of the Tour. The yellow jersey holder better not be having a bad day at that point."
Prudhomme said he was unconcerned that the London prologue would take place exactly two years after terrorist attacks on the city's transport network killed more than 50 people.
2007 TOUR AT A GLANCE
Starts London 7 July, finishes Paris 28 July
Six mountain stages, 11 flat stages
Three summit finishes
Two individual time trials
Two rest days
"London is a big city - it will do everything in its power to make things go smoothly. Every precaution will be taken, like for any big event.
"It is something tremendous. London is a well-run machine - it would have been ready in 2006."
Mayor of London Ken Livingstone said he was confident that his city could deliver a fitting start to the race.
"The Tour de France is so much more than just a cycle race, creating a carnival atmosphere wherever it visits.
"We want 2007 to be the greatest Grand Depart the Tour has ever seen, giving the riders a fantastic send-off as they start a gruelling three weeks racing."
No team time trial
One notable change from previous Tours sees the scrapping of the traditional transfer day that took the riders to the mountains at the end of the first week.
The first individual time trial will be staged at the end of the second week in Albi, and, like last year, there will be no team time trial.
Prudhomme said: "After the Alps, everything will still be up for grabs.
"We will have the answers later, because the difficulties for the riders will peak in the Pyrenees with the summit finish at the Col de l'Aubisque."
The opening 8km prologue will start near Trafalgar Square and finish on The Mall, while day two will see the riders travel out of London to Kent, finishing in Canterbury.
After leaving England, the 3,500km-long race dips into Belgium before heading to Burgundy and moving clockwise towards the Alps, where the first rest day will be taken in Tignes.
The riders will then head for the Pyrenees. The final, and potentially decisive, time trial will held on 28 July, the penultimate day of the Tour, over 55km between Cognac and Angouleme.
The traditional run in to the Champs Elysees will start outside Paris in Marcoussis, home of the French rugby union team's training camp, in recognition of the 2007 World Cup being held in France later in the year.
Full stage-by-stage run-down:
Saturday 7 July: prologue in London (8km)
Sunday 8 July: Stage 1 - London to Canterbury (203 km)
Monday 9 July: Stage 2 - Dunkirk to Ghent (167 km)
Tuesday 10 July: Stage 3 - Waregem to Compiegne (236 km)
Wednesday 11 July: Stage 4 - Villers-Cotterets to Joigny (190 km)
Thursday 12 July: Stage 5 - Chablis to Autun (184 km)
Friday 13 July: Stage 6 - Semur-en-Auxerrois to Bourg-en-Bresse (200 km)
Saturday 14 July: Stage 7- Bourg-en-Bresse to Le Grand Bornand (197 km)
Sunday 15 July: Stage 8 - Le Grand Bornand to Tignes (165 km)
Monday 16 July: rest day in Tignes
Tuesday 17 July: Stage 9 - Val d'Isere to Briancon (161 km)
Wednesday 18 July: Stage 10 - Tallard to Marseille (229 km)
Thursday 19 July: Stage 11 - Marseille to Montpellier (180 km)
Friday 20 July: Stage 12 - Montpellier to Castres (179 km)
Saturday 21 July: Stage 13 - individual time trial Albi (54 km)
Sunday 22 July: Stage 14 - Mazamet to Plateau de Beille (197 km)
Monday 23 July: Stage 15 - Foix to Loudenvielle-Le Louron (196 km)
Tuesday, July 24: Rest day
Wednesday, July 25: Stage 16 - Gourette to Col d'Aubisque (218km)
Thursday, July 26: Stage 17 - Pau to Castelsarrasin (188km)
Friday, July 27: Stage 18 - Cahors to Angouleme (210km)
Saturday, July 28: Stage 19 - Cognac to Angouleme (55km time-trial)
Sunday, July 29: Stage 20 - Marcoussis to Paris, Champs Elysees (130km)
Total distance 3547km (2205 miles)