Berlin  - Just 1.8 kilometres long, but costing a whopping 320 million euros (459 million dollars), Berlin's newest underground railway line (U-Bahn) opened on Saturday, linking the city's central station with the famous Brandenburg Gate, just three minutes away.

The new line, dubbed the "Chancellor's Railway," because it passes under Berlin's government quarter - took 14 years to build, and has only three stations.

The U-55 line fills a important gap in the city's public transport network however, as the central station had no underground station previously.

As the line also passes under what was once the no-man's-land between the divided East and West Berlin, the U-55 is set to play a role in commemorating the city's separation by the Berlin Wall between 1961 and 1989.

On the first departure Saturday of the distinctive yellow trains, Berlin Mayor Klaus Wowereit called it "the U-Bahn of Unity," and said "If the wall had not fallen ... this U-Bahn line would never have been built."

Exhibition spaces, audio-visual screens other media at the Brandenburg Gate station are to bear witness to the city's past.

"With the celebrations for the 20th anniversary of the fall of the Berlin Wall, we are giving passers-by the opportunity to inform themselves at one of the hot-spots of German history," said Minister of State Bernd Neumann.

The line took so long to build partly because of disagreement between the cash-strapped city of Berlin and the federal government over who should pay for the construction. The three-station section which opened Saturday is the first segment of a longer line due to run to Alexanderplatz in the former east of the city, to be completed by 2017.

On the first day of operation, passengers were permitted to travel free of charge. (dpa)