IF Antirhodos disappeared 1600 years ago how did Franck goddio know antirhodos existed?​

Franck Goddio knew that Antirhodos existed because he carried out numerous archaeological investigations at the seas, in which he found this island. Goddio's investigations were motivated by numerous ancient writings that mentioned the existence of this island in the vicinity of Alexandria.

Antirhodos Island was an island in Egypt in the Mediterranean Sea, next to Alexandria, of which in ancient times it was part of. Today it is submerged in the port of the modern city. It is probable that the palace of Cleopatra was located on the island. The island, as well as part of the ancient city, sank in the sea after earthquakes and rising sea between the 4th and 8th century. They were found after investigations in 1996 that are still ongoing.

i dont know i didnt take the test