Regnery Publishing uses the Porta Nigra on its logo because the Regnerys are from Trier. Many, if not most on this board have read books published by Regnery.
I do have a number of Regnery books on my shelves.
That was an interesting point about their logo — how did you learn of that?!
Visited Trier several times when I was stationed at Spangdahlem AFB in 1971. Porta Nigra was very interesting. Excavation of more Roman ruins was continuing and I've always wondered what else they discovered.
On another note, the Schieffer Keller was a cool place to visit in Trier. It's a restaurant, located many feet below the street level but once the entrance was at street level. It was originally used as a warehouse a couple of hundred (or more) years ago. However, with the destruction of Trier during centuries of different wars it became buried. After WWII it was rediscovered and made into a resturant.