Limburg juts south into Belgium like a wedge driven between the rest of the Netherlands and the rest of the world. Its long eastern flank is the border with German North Rhine-Westphalia. To the west is Belgian Limburg. The river Meuse - the Maas - traces a section of that western border. The shape on a map looks accidental, but every angle of it was negotiated. The 1839 Treaty of London split a single old Belgian-controlled province between Belgium and the new Kingdom of the Netherlands, and Limburg has been the Dutch leftover ever since. To appease Prussia, which had lost its own access to the Meuse, the new Dutch province was joined to the German Confederation between 1839 and 1866 as the Duchy of Limburg. Even when that ended, the title 'Duchy of Limburg' stayed in official use until 1907. The head of the province today is still addressed as Governor instead of King's Commissioner, the way every other Dutch province does it. The province remembers.

Limburg has been a place that mattered to people who lived elsewhere for a very long time. Julius Caesar conquered it in 53 BC and wrote that he had extinguished the name of the Eburones who had revolted under Ambiorix. The Roman Via Belgica cut east-west across South Limburg, connecting Tongeren to Cologne, and Mosa Trajectum - Maastricht - and Coriovallum - Heerlen - were founded along it. The Carolingian dynasty came from this region; Charles Martel was born just south of here in Herstal, and Charlemagne made Aachen, whose suburbs now sprawl into South Limburg, the capital of his empire. When the Frankish lands were split after Charlemagne's death, the 870 Treaty of Meerssen - signed in a South Limburg village - divided Lotharingia along the Meuse itself. The river that runs through the province has been a border since the ninth century. Some borders age into invisibility. This one did not.

For most of the nineteenth century South Limburg was farmland. The Industrial Revolution that transformed the rest of Europe largely passed it by. Then in 1893 coal mining became practical here, and from 1901 the Dutch state set up the Staatsmijnen to develop the seams the private sector could not finance alone. For sixty years the eastern mining district around Heerlen-Kerkrade-Brunssum and Sittard-Geleen was the industrial engine of southern Netherlands. Then in the period between 1965 and 1975 the mines closed - sixty thousand jobs in this corner of the country, gone within a decade. The Dutch government moved several big state agencies - the pension fund ABP, the statistics bureau CBS - down to Heerlen to soften the blow. It softened it, but did not fix it. The mines did not just provide employment. They had organised an entire regional identity: shifts, parishes, miners' choirs, fanfare bands, particular kinds of housing, particular kinds of pride. When the shafts closed, all of that had to find something else to be.

Limburgish has been an officially recognised regional language since 1997, under Chapter 2 of the European Charter for Regional or Minority Languages. About 1.6 million people speak it across Dutch Limburg, Belgian Limburg and the German border region - and almost every town and village has its own dialect, with isoglosses cutting across the province in such density that no single version can be called canonical. The province is overwhelmingly Catholic in a country that is overwhelmingly not, and Carnaval - three days of costumed parades and the temporary deposition of mayors by a substitute called the Prins - is observed with a seriousness that has more in common with the Rhineland than with Amsterdam. The food is different too: vlaai, the broad open-faced fruit tart shared at funerals and birthdays, is a Limburg signature. The mood is different. People will tell you the south is gemoedelijk - genial, easy-going, less hurried than the Randstad - and they will say it in a tone that quietly disputes whether the Randstad really speaks for them at all.

At the Vaalserberg the borders of three countries meet at a single point. Climb the watchtower and you can stand in three nations at once. Down at the bottom of the province, in December 1991, European leaders met in Maastricht and agreed the treaty that turned the EC into the European Union - formally signed by foreign ministers in February 1992. The Treaty on European Union is more often called the Maastricht Treaty, after the city. There is a tidy symbolism in the fact that the document founding modern Europe was signed in a Dutch city that has spent its history being argued over by everyone around it - and that the province it sits in is the one place in the Netherlands where standing in three countries simultaneously is geographically possible. Limburg is the southernmost province on the map. It is also, in a curious way, the most European one.