Carthage itself was absolutely ploughed in excess of, but the concept of it being salted does not convert up right up until the nineteenth century. Carthage was likely not salted after the Third Punic War, and neither was Milan by Frederick Barbarossa around a thousand yrs afterwards. The notion appears to arrive from confusion about a Medieval buy contacting for the city of Palestrina to be ploughed above "like Carthage", and also salted.