> The U1 line in Berlin was constructed between 1902 and 1926.
There's also the S1 line, large parts of which date back to 1874[0]
or even 1838[1], depending on how you count: The train back in 1838 established most of the path today's S1 takes through southwestern Berlin. The S1 runs on a second pair of rails, constructed in 1874, that run in parallel to the 1838 line and diverge from it near the city border. The old 1838 line is set to be rebuilt by 2038.
There's also the S1 line, large parts of which date back to 1874[0] or even 1838[1], depending on how you count: The train back in 1838 established most of the path today's S1 takes through southwestern Berlin. The S1 runs on a second pair of rails, constructed in 1874, that run in parallel to the 1838 line and diverge from it near the city border. The old 1838 line is set to be rebuilt by 2038.
[0]: https://en.m.wikipedia.org/wiki/Wannsee_Railway
[1]: https://en.m.wikipedia.org/wiki/Berlin%E2%80%93Magdeburg_rai...