The Millau bridge over the River Tarn in the Massif Central mountains is more than 300m (984ft) high – taller even than the country’s Eiffel Tower.
The bridge, which opens to traffic on Thursday, was built to clear summer traffic jams around the town.
The BBC’s Paris correspondent, Caroline Wyatt, says the bridge is one of the most breathtaking ever built.
She says that with its concrete and steel pillars soaring high above the morning fog in the Tarn Valley, the construction makes a spectacular sight.
‘Delicacy of a butterfly’
Seven slender piers support the roadway, rising into seven graceful pylons bound to the bridge with what look like cobwebs of steel, our correspondent says.
“The bridge is just on the clouds,” Millau Mayor Jacques Godfrain told the BBC’s World Today programme.
“The architect, Norman Foster, gave us a model of art.”