Well, that was quick.
The largest European city without a U.S. namesake seems to be Istanbul, population 9 million and change. (There’s not even a Constantinople, though there are a couple of Constantines.)
The largest European capital without a U.S. namesake is Bucharest, population about 2 million, assuming that Kief, North Dakota covers Kiev (or Kyyev, as it’s now apparently spelled).
The most famous European city without a U.S. namesake is Pisa, especially if we assume that the many “Frankforts” stand in for Frankfurt.
A reader supplies a complete list:
Andorra la Vella, Bratislava, Bucharest, Chisinau, Helsinki, Ljubljana, Luxembourg, Minsk, Nicosia, Podgorica, Reykjavik, Sarajevo, Skopje, Tallinn, Tirana, Vaduz, Valletta, Vilnius, and Zagreb
Other cities: Arhus, Graz, Tampere, Mannheim, Duesseldorf, Espoo, Dortmund, Wuppertal, Duisburg, Bielefeld, Leipzig, Linz, Gothenborg, Bochum, Nantes, Bologna, Kirklees, Bilba, Rennes, Wolverhampton, Basel.
I note with regret that there’s also no Konigsberg (famous for Kant and the Seven Bridges) in the U.S.
I note with even greater regret that there’s no longer a Konigsberg in Europe, either.
My original post failed to ask contestants to indicate whether they wanted to be identified. I’ve taken the safer course, but if you want to claim the honor you deserve, please let me know.
Thanks to all.