I plan to reject these two, as I think they are (former) city gates not strict triumphal arches:
- Trier Porta Nigra
- Istanbul Golden Gate

And one I'm in doubt about:
Vienna Hofburg Outer Castle Gate (I know it's mentioned in Wikipedia but what is it) ???
-> is this the red-black Swiss Gate? and is that a gate or a triumphal arch?

If I'm wrong, please tell me and show some form of 'proof'

The Heldentor in Vienna used to be the main entry from the newly designed Ringstrasse to the Hofburg (in which sense it shouldn't be considered a triumphal arch). It was built in the 19th Century and is outside the Hofburg itself. It is not identical with the Swiss Gate which is Renaissance and within the Hofburg (and not in the form of a triumphal arch).
See on the right side of: http://www.flickr.com/photos/romai/2479785939/