the thriving city? thriving underwater all this time? Who knew.
Atlantis was a myth created by the Atlantic civilization (the megalith builders) to protect their trade routes by misdirecting seekers into the open ocean from which few returned.
“Atlantis” was right if front of the explorers, but they had it on ‘good authority’ from the local peoples (who later became the Phoenicians) that the city was on an Island far out at sea.
The Phoenicians were from the present-day Lebanon region. They founded Carthage and other cities in the far-western Mediterranean, which may be what you are thinking of.