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The Treaty of Concordia (1648): how one island came to have two sides

On 23 March 1648, the French and Dutch governors of Saint Martin signed an agreement that gave each nation its own part of the island. Here is who signed it, what it settled, what it left open, and why it still shapes daily life.

By SXM Daily ·

Last checked: 14 October 2026

Next check: 14 October 2027

On 23 March 1648, the French and Dutch governors of Saint Martin put their names to a short agreement that gave each nation its own part of the island. That agreement, known as the Treaty of Concordia, is the reason one small island today has two governments, two currencies and two legal systems.

A map of part of St. Martin from an 1863 book, marking the French and Dutch parts of the island with Marigot, Fort Louis and Fort Amsterdam

Photo: R.F. van Raders (1863), digitised by the British Library / Wikimedia Commons, Public domain

Who signed it

Two governors signed the agreement, each acting for a different European power:

  • Robert de Lonvilliers, governor of the island for the King of France
  • Martin Thomas, governor of the island for the Prince of Orange and the States of Holland

Officers from both sides added their signatures. The full French text of the treaty, published by the CEFAN research centre at Université Laval, gives all of their names.

Where it was signed

The text says the agreement was made on a hill it calls the mount "des Accords", meaning the hill of the agreements. That is where the name Concordia comes from.

Which hill that was, in today's landscape, is a separate question. We have not found an official source that confirms the modern location, so we don't name one here.

What the agreement settled

The treaty is short, and its first two articles deal with who lives where.

  • Article 1, the French part. The French would stay in the quarter where they were already living, and would take the whole side of the island that faces Anguilla.
  • Article 2, the Dutch part. The Dutch would keep the quarter of the fort, with the land around it, on the south side of the island.

In other words, the agreement started from the facts on the ground. Each group kept the area it already occupied, and the French side was described by the direction it faced rather than by a line on a map.

What it left open

The treaty did not draw an exact border.

  • Article 8. The precise limits between the two nations were to be worked out later. The matter was referred to the French General and to the Governor of St. Eustatius, with deputies to be sent to visit the area before the two quarters were divided.
  • Article 9. Until then, neither side was allowed to build fortifications. Doing so would count as breaking the agreement.

This article covers the 1648 text only. It does not go into how or when the border was later marked out.

Why it still matters

UNESCO, describing the island in its Memory of the World register, says Saint Martin is connected to both the Netherlands and France through the Treaty of Concordia. The Dutch side, Sint Maarten, covers about 16 square miles. The French side, Saint-Martin, covers about 21 square miles.

That split shapes everyday life:

  • Two governments. Sint Maarten, the Dutch side, and Saint-Martin, the French side, are each run by their own government.
  • Two currencies. Prices on the Dutch side are in Caribbean guilders (XCG). The French side uses the euro (EUR).
  • Two legal systems. Each side has its own laws.

Anyone who lives, works or does business on both sides deals with the results of the 1648 agreement every day.

FAQ

Q: When was the Treaty of Concordia signed?

A: On 23 March 1648.

Q: Who signed it?

A: Robert de Lonvilliers for the King of France and Martin Thomas for the Prince of Orange and the States of Holland, along with officers from both sides.

Q: Where does the name Concordia come from?

A: The treaty says it was signed on a hill called the mount "des Accords", the hill of the agreements.

Q: Which part of the island did the French get?

A: The quarter where they already lived, plus the whole side facing Anguilla.

Q: Which part did the Dutch get?

A: The quarter of the fort and the land around it, on the south side.

Q: Did the treaty set an exact border?

A: No. Article 8 left the exact limits to be settled later.

Q: How big is each side?

A: According to UNESCO, the Dutch side is about 16 square miles and the French side about 21 square miles.

Sources

  • https://axl.cefan.ulaval.ca/amsudant/traite_1648_stmartin.htm
  • https://www.unesco.org/en/memory-world/route/root-freedom-case-study-how-enslaved-africans-gained-their-freedom-dual-national-island-sint

Source: https://axl.cefan.ulaval.ca/amsudant/traite_1648_stmartin.htm

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