Wikipedia
Antirhodos (sometimes Antirrhodos or Anti Rhodes) was an island in the eastern harbor of Alexandria, Egypt, on which a Ptolemaic palace was sited. The island was occupied until the reigns of Septimius Severus and Caracalla and it probably sank in the 4th century, when it succumbed to earthquakes and a tsunami following an earthquake in the eastern Mediterranean near Crete in the year 365. The site now lies underwater, near the seafront of modern Alexandria, at a depth of approximately .
Descriptions of the island were recorded in classical antiquity by Greek geographers and historians. Strabo described a royal house on Antirhodos in 27 BC and wrote that the island's name ("counter-Rhodes") derived from the island's rivalry with the island of Rhodes. Antirhodos was part of Alexandria's ancient royal port called the Portus Magnus, which also included parts of the Lochias peninsula in the East and the island of Pharos in the West. The Portus Magnus was abandoned and left as an open bay after an earthquake in the 8th century.