Which country does France share its longest border with?

Ask anyone to name France’s neighbours and you will hear Spain, Italy, Germany, Belgium, Switzerland. All correct. But the longest border France has with any country does not touch Europe at all. It runs through the Amazon rainforest.

The short answer

France’s longest land border is with Brazil. It separates French Guiana, an overseas region of France on the north-east coast of South America, from the Brazilian state of Amapá. The border is about 730 km long. The France–Spain border, the longest one in mainland Europe, comes second at about 623 km. A French Senate report describes the Brazilian frontier as the longest land border France has.

The real story

French Guiana is not a colony in the old sense. It is an overseas region of France, so when you cross from Brazil into French Guiana, you are technically crossing into France.

Part of the frontier follows the Oyapock River (Oiapoque in Portuguese). Only one bridge crosses the border, the Oyapock River Bridge, linking the town of Saint-Georges on the French side with Oiapoque on the Brazilian side. Much of the rest of the line runs through dense rainforest. That makes it a very different kind of frontier from the mountain passes of the Pyrenees: fewer ski resorts, considerably more rainforest, and far fewer tourists queuing to cross it.

The border has a long and argumentative history. Its legal basis goes back to the Treaty of Utrecht of 1713 between France and Portugal, which named a river called the Japoc as the boundary. The trouble was that nobody agreed which river that was. France argued it meant a river much further south, the Araguari, which would have given France a big slice of territory. Brazil said it meant the Oiapoque.

The squabble lasted nearly two centuries. It was finally settled by international arbitration in Switzerland in 1900, and the ruling went in Brazil’s favour, fixing the boundary at the Oiapoque. A small cultural echo survives: some Amerindian communities in Amapá still speak a French-based creole.

Why people get it wrong

Most of us think of France as a hexagon-shaped country in Western Europe, full stop. Its overseas regions rarely appear on the maps we grew up with, and when they do they tend to be shoved into little boxes in the corner.

So when we picture France’s borders, we picture its European neighbours. Spain is the natural guess because the Pyrenees make such a long, memorable frontier. Very few people stop to remember that France also has a sizeable chunk of South America, and that its biggest neighbour there is the biggest country on the continent.

“France’s longest border has jaguars on one side and baguettes on the other. Try fitting that on a postcard.”