Aboard the Warsaw-Berlin Express ? Once upon a time, when rail travelers crossed the Polish-German frontier, their passports and belongings were scrutinized by stern Polish and German border police. Even in the 1990s, it felt like a movie from the 1930s.

These days, the Polish police are gone for good. The Germans are taking a long coffee break.

During a recent westbound trip, two German border policemen got on the train at the frontier. They headed straight for the first-class coach and sat down. One read the newspaper; the other plunged into a romantic novel. They didn’t look up until two hours later when the train rolled into Berlin.

Asked if they were going to check anyone’s passport, the one reading the newspaper replied with a curt “nein.”

This is the new “borderless Europe,” where it is possible to hop on a train or bus and travel from Portugal to Poland without showing your passport to anyone. Most of the frontier border posts in Western Europe have been gone for nearly a decade. Europe’s eastern half is rapidly catching up. Only the gentle beeping of your mobile phone – and the arrival of a text message telling you that you’ve entered a new service area – lets you know that a national border has been crossed.

In the wake of the 20th Century’s two world wars, which saw the rival powers of Europe invade, bomb, occupy and otherwise devastate each other’s territory, the grand experiment of doing away with internal borders is, quite simply, astounding.

One of the European Union’s guiding principles is “the free movement of people” across the borders of its 27 member states. Principle became reality in 1995 with the implementation of the Schengen agreement to eliminate border controls between seven countries in Western Europe. The list of countries joining the Schengen Zone has increased steadily since. Britain and Ireland are the notable hold-outs.

Last December, nine members were added – Poland, the Czech Republic, Slovakia, Hungary, Slovenia, Estonia, Latvia, Lithuania and Malta. The zone now stretches from the Atlantic to the EU’s border with Russia, a territory of 1.65 million square miles and 400 million people.

Traditionally, European borders have been symbols of state sovereignty and order. Mountains and rivers formed logical borders, but where nature was insufficient, statesmen and tyrants drew lines on maps, often with little regard to logic or nature.

Language and ethnicity became another basis for defining borders, but sometimes communities were so intermingled, no border made sense. This remains true in Eastern Europe, where some very old people boast that they have lived in half a dozen countries while never leaving the village of their birth.

The end of World War II led to the harshest division of Europe as the Iron Curtain split the continent in half. Germany was divided into East and West; a wall bisected Berlin, the capital.

Behind the Iron Curtain, the facade of socialist harmony concealed some of the continent’s least hospitable borders. The German-Polish border along the Oder River was always one of the nastiest. (Today’s anomaly of German border police boarding the train from Poland has more to do with job security for the officers than border security for the German nation.)

The Hungarian-Czechoslovak border also had a chilly Cold War history. The Danube River forms part of the boundary between Hungary and what is today Slovakia, but the main crossing point, the Maria Valeria bridge linking Esztergom in Hungary with Sturovo in Slovakia, was destroyed in 1944 by the retreating German army.

After the war, communist authorities on both sides of the Danube decided to leave it that way. It was not repaired and reopened until 2002, when Slovakia and Hungary were seeking admission to the EU.

Before the bridge’s reopening, the only Danube crossing between the two countries was the bridge linking the sister cities of Komarno and Komarom.

A large Hungarian community lives on the Slovak side of the river; in the Slovak city of Komarno, Hungarians are the majority. When the pro-Moscow populist Vladimir Meciar came to power in Slovakia in the early 1990s, he strengthened his power base by stirring up resentment against the Hungarians.