This was an ancient city near the modern city of Tunis in the country of Tunisia on the northern coast of Africa. It lay directly across the Mediterranean from Italy, and was often at war with the Roman Empire.
The African Muslim populated drove the Romans out of Africa when they laid siege to and ultimately destroyed Carthage in about 700 AD. It was never rebuilt.
It was eventually overtaken by Tunis as that city expanded. Ruins still remain around the now-neighborhood of Carthage in Tunis, and many are UNESCO Heritage Sites.
Why I Looked It Up
I’m reading a book about the Roman Empire, and it comes up a lot. Several of the characters are at war with the Numidian Empire in Africa, which occupied the north coast of Africa, of which Carthage would have been a part.