Kōnstantinoúpolis (Κωνσταντινούπολη) is a standard compound of his name (Kōnstantínos) and the suffix for city (pólis), meaning “City of Constantine.”
In Old French the Greek suffix -polis dropped the “-is” and softened the “p” into a “ph” or “v” sound, eventually collapsing into -ople. Kōnstantinoúpolis became Constantinople in French.
English borrowed the word completely intact from the French spelling and pronunciation
You see the same fir Adrianople.
The American cities are modern
Thank you. As I said, I’d wondered. The only correction I’d make is that many ancient cities such as Heliopolis and Neapolis, indeed the Acropolis, and tons of places that Alexander modestly named Alexandropolis are referred to in English with that suffix. Constantinople and, as you pointed out, Adrianople are exceptions. Your explanation makes sense and I appreciate receiving it