Germany - Mainz

Mainz
Die schone Stadt am linken Rheinufer gelegen, einst alter Kurfürsten - u. Erzbischofssitz, gruBt gegenüber der Mainmundung kulturell und historisch ihre Gaste.

This translates something like this:
The beautiful town on the left bank of the Rhine located, once old electors - and Archbishop seat, greets opposite the mouth of the Main culturally and historically their guests.

St Stephan und (and) St. Martin

This postcard is postmarked on the 11th of December in 2013 from Germany.  So the date (in Europe) would be written 11-12-13.

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Mainz was founded as a military post by the Romans in the late 1st century BC.