“After the war, the cities turned away from each other,” said Ryszard Bodziacki, the mayor of Slubice (pronounced swoo-BEE-tseh), once part of Frankfurt an der Oder, the eastern German city not to be confused with the better-known Frankfurt am Main in the west. Mr. Bodziacki is working with his counterparts across the Oder to reintegrate the two cities, whether through joint work by police forces and fire brigades or by sending Polish children to German schools.  That cooperation will be easier in practice starting Friday. The border controls are ending because Poland is officially joining the borderless zone within the European Union known as the Schengen area, named for the town in Luxembourg where in 1985 a group of Western European countries signed the first agreements to open their boundaries.  Now Poland and eight other countries, most from the former Soviet sphere of Central and Eastern Europe, have adopted the common visa, asylum and external border procedures required for membership. The police will still patrol inside their borders. But once the new members have joined, it will be possible to drive clear from Lisbon, Portugal, to Tallinn, Estonia, without taking out a passport or identity card.  The movement from east of the common border has caused jitters in Germany, where the police have protested what they say will be a surge in crime in Germany once controls at border posts cease.  Crime gravitates toward open borders, their union representatives say, and the earnings gap between Germany and its poorer neighbors like Poland and the Czech Republic tempts criminals. Josef Scheuring, chairman of the federal-police union that organized the protests, said the change had happened on a political timetable.  Politicians made decisions before the technical side could be worked out, on issues like the delayed upgrade to the Schengen information-sharing network and the harmonization of radio frequencies between the German and Polish police. “Greater Europe will only be accepted by the people if it is safe,” Mr. Scheuring said.  But with seeming unanimity, Poles say they view their country’s entry as proof that they have achieved an equal footing with their partners to the west.  “This border is well protected,” said Andrzej Adamczyk, deputy director of the Polish border guard’s border-management office. He pointed out that European Union officials had approved the guard’s work, which included investments in night-vision technology, cameras and new vehicles.  The German news coverage of the border opening, what there is of it, has largely been about Germans’ installing metal shutters, putting up barbed wire and even buying guns. But in conversations with local residents along the way, the fortifiers seem to be a vocal minority rather than part of a popular groundswell.  “It’s reasonable to let people live and travel freely,” said Christian Pfeiffer, 30, a psychologist, who was out with friends at a Christmas market in the German border town of Görlitz.  Even before now, the border was only a minor nuisance, crossed easily by Germans and Poles for cheaper gasoline or cigarettes, or to go to work. In most cases, citizens of the European Union have passed through the checkpoints with little more than a flash of an identity card, no passport necessary.  “I think it’s a good thing,” said Monika Kraska, 22, a hairdresser in Slubice. “There won’t be any queues.” German clients visit the tiny salon where she works for inexpensive haircuts.  Notably absent from the discussion is the long-expressed fear that Poles will pour across the border to snatch German jobs. That is not just happenstance. When Poland joined the European Union in 2004, Germany left significant legal hurdles in place to prevent its neighbors from coming to work.  Instead, many ambitious, highly mobile Polish workers moved to more welcoming parts of Western Europe — Britain and Ireland in particular — where they have been credited with fueling economic growth, passing through Germany, especially its poorer, depopulating east, on the way.  A version of this article appears in print on , on Page A4 of the New York edition with the headline: Once Volatile, Crossing Is Opening With a Whisper. Order Reprints| Today's Paper|Subscribe
As of 12:01 a.m. on Friday, the border between Poland and Germany, one of the most violently contested frontiers on earth, was opened for traffic.