It runs through Baden, from Mannheim via Heidelberg, Karlsruhe, Offenburg, Freiburg, Basel, Waldshut, Schaffhausen and Singen to Konstanz.

The Baden Mainline is 412.7 kilometres long, making it the longest route in the Deutsche Bahn network and also the oldest in southwest Germany.

The Upper Rhine Valley has been an important trade route from Central Europe to Switzerland and Italy since Roman times.

George Stephenson’s locomotive and the opening of the line between Liverpool and Manchester was first discussed in the Baden Parliament by the priest and liberal politician Gottlieb Bernhard Fecht (1771–1851) in the autumn of 1831.

[1] The first real initiative for a railway was made in 1833 by the Mannheim businessman Louis Newhouse, but just like the suggestion of Friedrich List, it was not supported by the Baden government.

A specially convened meeting of the Baden Assembly of the Estates (Badische Ständeversammlung) decided in 1838 to build a railway from Mannheim to the Swiss border near Basel at public expense, as had been called for on 31 July 1835 by the Freiburg historian Karl von Rotteck.

The ongoing construction to the Swiss border was disrupted by the events of the March Revolution and the course of the line was damaged at several points by guerrillas.

It could not, however, insist on its preference and the continuation of the main line from Baden to Konstanz, opened on 13 June 1863, ran from Waldshut not through Jestetten, but via Erzingen and Beringen.

In the north connections were established in Heidelberg to the Main-Neckar Railway towards Darmstadt and Frankfurt in 1846 and in Mannheim to Ludwigshafen, Mainz and Cologne in 1867.

On 22 July 1870, the mobilisation for the Franco-Prussian War made the main line unusable by the public at several points between Rastatt and Offenburg.

It soon became apparent, however, that the other Central European states had chosen standard gauge, which would have left the Baden railway network isolated.

Therefore, Mannheim tried to provide a direct rail connection to the south and sought to build a railway to Karlsruhe via Schwetzingen.

Due to the growing traffic between Mannheim and Basel and the growth of cities it had become necessary to remodel the major rail nodes.

After Alsace had returned to France after the First World War, all German trains ran to Basel on the Baden main line.

During the occupation of the Ruhr, French troops occupied Offenburg and Appenweier in February 1923, so traffic was stopped on the main line and trains had to be diverted over a large area.

The Orient Express also operated over the Baden main line: coming from Strasbourg, it ran on the route on the section between Appenweier and Karlsruhe.

During the Second World War, the Baden main line—like all major lines in Germany—was affected by heavy bombardment of railway junctions and the destruction of bridges and buildings.

Since the single-track section became a bottleneck on this heavily used route, the second track was restored in 1950 at the insistence of Switzerland, which considered that the congestion endangered the approach to the Gotthard Pass.

In the 1980s, the Basel–Waldshut section of the line was duplicated to provide improved local services on an integrated regular interval timetable.

Congestion was relieved on the northern section of the main line between Mannheim Baden and Bruchsal with the opening of the Mannheim–Stuttgart high-speed railway in stages between 1987 and 1991.

It runs almost straight across the Upper Rhine Plain and originally only had a single intermediate station at the halfway point in Friedrichsfeld.

Meanwhile, the Heidelberg freight yard and the locomotive depot were closed and only one pair of tracks of the four-track railway between Friedrichsfeld and Wieblingen is currently in use.

The section of line between Heidelberg and Karlsruhe runs along the eastern edge of the Upper Rhine Valley from north to south.

In Weingarten, Untergrombach and Bruchsal Bildungszentrum, the platform heights were raised to 55 cm for step-free access to the Karlsruhe Stadtbahn trains.

At all stations between Bruchsal and Heidelberg the platform heights were raised to 76 cm for step-free access to the Rhine-Neckar S-Bahn trains.

While the line is mostly straight, it has, in the southern section between Schliengen and Efringen-Kirchen a winding route passing between the Rhine and the Isteiner Klotz ridge above the villages on the slopes of the Black Forest.

In 1971 there was an accident at Rheinweiler when an express train that was running too fast on the twisty section between Efringen-Kirchen and Schliengen road was derailed and crashed down the railway embankment.

In addition to Deutsche Bahn AG, Swiss Federal Railways operates one third of all freight trains on this route, especially as combined transport.

Switzerland agreed not to impose tariffs on freight in transit or to subject trains on the line to customs formalities.

Therefore, the military sought the creation of bypasses around the two sections running through Switzerland so that there would be to a secure east–west supply route through southern Baden during wartime.