There may be several different contenders for this title but the most obvious is the Light of the World that is one of the Seven Wonders of the Ancient World. In this case it is The Pharos, the lighthouse at Alexandria in Egypt. Built in the 3rd century BC its purpose was as a guide to shipping in this important port, but it collapsed as the result of an earthquake in the 14th century. It was rediscovered using ultrasound archaelogical underseea investigation in the last centrury.