St. Stephen's Cathedral, Vienna, Austria
St. Andrew is identified by the name in his halo. But the image portrait eschews the wild hair, long beard, and long cross that usually identify this saint. He does have the traditional book, but so do most images of apostles, preachers, etc.
The cathedral was begun and completed during the 14th century, so the window may be of the same era, but it is possible that it might be as late as the 15th.
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Read more about St. Andrew.
Photographed at the cathedral by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.