@ bayern klassisch [#34]

It's my belief that it went through Switzerland to avoid the French postal system which would have transited Paris. That city had been under siege and occupation. Being posted in Switzerland guaranteed the letter would arrive in Berlin in "normal" delivery time.

The reverse only shows a delivery date stamp 8/2 also 9 1/2 NM in 21mm circle.

Here are two letters addressed to southern France routed to avoid German occupied areas. They were both posted in Basel, Switzerland. Though they are not from Switzerland to German states, they seem to fit into this discussion. Maybe?

Originated 14 January 1871 St Amarin, France
posted Basel 18 January,
transit Lyon 19 January, no arrival marks.
Of special interest, the stamp has no perforations and was previously used [cut from another letter]. It is still glued to the original paper. Though very light, the date on the stamp can be read and is the same as the Basel to the left.



The second originated in Brussels dated 4 February 1871, posted Basel 6 February, transit Suisse Amb. Marseilles 7 Feb, arrived Cette 8 February on the reveres. Also on the reverse is a Basel forwarding agent Wenk & Plüss oval mark.