By Chris Bockman BBC, Millau

It is neither very wide nor very deep, but it has provided an opportunity for France to launch another costly and bold "Grand Projet".

Cars will travel 245 metres above the Tarn Valley on the Millau Bridge

Five-hundred workers are busy putting up the world's tallest bridge in the backyard of anti-globalisation protester Jose Bove.

It will stretch across a 2.5km wide valley on the southern edge of the Massif Central mountain range.

The highest pillar will stand at just over 340 metres (1,115ft) tall. The carriageway itself will be 245 metres off the ground.

The bridge will eventually form part of the A75 motorway linking northern Europe to the south. It is due to open early 2005.

Eiffage, the company building this bridge, also built the Eiffel Tower.

From both sides of the valley the metal sections of the bridge are assembled, lifted slightly and then in an elaborate manoeuvre pushed into place on each of the seven supporting pillars.

Find out more about the Millau bridge At-a-glance

Like Concorde and the Channel Tunnel, this bridge is Franco-British.

The world-renowned architect Norman Foster is behind the design.

He was treated like visting royalty during a flying three-hour trip to see for himself how the project is progressing.

"I think it's heroic, it's extraordinary," he told BBC News Online.

"To have discussions, conversations, studies and models and then to see that being translated into reality in this landscape is an extraordinary experience and I think it touches everyone."

The company set itself a deadline of three years to build the bridge.

Then it has 75 years to recover its 260 million euro ($300m) investment by collecting receipts from a bridge toll.

But even the best engineers' plans can go awry.

Weather conditions in this part of France can be pretty harsh and that has put work on the bridge behind schedule.

The heatwave over the summer meant some of the welding couldn't be done, and over the previous winter it was so cold some work had to be halted.

Without the bridge, many motorists heading to the south of France go through the small town of Millau.

The town has only has a few thousand residents - including Mr Bove on his nearby cheese farm - but it can take four hours to get through in the height of summer.

While motorists will be happy to avoid the town, small business owners in particular fear they could lose passing trade as cars bypass the town.

Jose Bove's views on the bridge are not known

But the town's mayor, Jacques Godfrain - a former government minister and close ally of President Chirac - used all his political influence to get permission for the bridge to be built and overcome local opposition.

"When they built the Eiffel Tower there were some people against it and at the time they engaged to destroy it," he said.

"But today if you want to destroy the Eiffel Tower nobody would support you. The same thing goes for many other monuments in the world."

The mayor is gambling that critics will go quiet as people head to the area just to see the bridge.

In fact they already are. It has become a tourist attraction in its own right.

An estimated 100,000 people have made a detour to peer up and marvel at the unfolding spectacle.