What makes you think Carthage's location was ever lost? The whole salting the earth thing is a Victorian myth that appears in none of our texts. Archaeologically we know that there was some, greatly reduced, settlement at the site of Carthage even after 146. Gaius Gracchus, only a couple decades later, founded Carthage as a colony and began rebuilding at the site. His colony was abolished shortly afterward but Caesar began establishment of a colony there and at Corinth beginning in 45 but was murdered before it was completed. The work on the colony was completed by Augustus and by the middle of the Principate Carthage was the second largest city in the western part of the Roman state, possibly second only to Rome in the entire state as a whole. The site was incredibly important in the early church and the Vandals made it their capital after capturing it--it was subsequently retaken by the Eastern emperors and served as the capital of the prefecture of Africa. It was finally destroyed after a number of struggles during the Islamic conquests, and replaced in importance by Tunis--but its location was never forgotten