On its side of the bridge, France built a border police post, to manage customs and immigration services, that already appears weather-beaten and worn. On the bridge, which is more than four football fields long, the double white line at the center of the pavement is peeling away.

But on the Brazilian side, things lagged. Brazil had pledged to pave the 360-mile dirt road to Macapá, the capital of Amapá State, from Oiapoque (pronounced oh-ya-POHK), the town on the Brazilian side of the bridge. But much of the highway has yet to be paved. Brazil also delayed customs and immigration facilities, completing the structures only recently. They have yet to be furnished and supplied with computers and other necessities.

“We could open the bridge tomorrow if they would send personnel and if they finished the work,” said Éric Spitz, the prefect of French Guiana, during an interview in his large, wood-lined office in Cayenne, the capital, a three-hour drive from St.-Georges.

In Oiapoque, no sign marks the road that leads to the bridge. The newly completed buildings, with bright white walls and blue roofs, stand in the middle of a red dirt field. Cows and goats graze nearby. A flimsy barrier of barbed wire blocks the way, and a yellow sign in Portuguese reads: “Stop. Identify yourself.” Two dingy white dogs, stained ocher from rolling in the red dirt, sleep on the road.

“It’s not permitted to enter,” a genial security guard said. His tiny guard shack had no electricity or running water. A sign on it read, “Smile, you’re being filmed.” But the guard, who would not give his name, said there were no cameras. “It’s just for show,” he said.