I don't know if this discovery "will change history forever", but it is definitely a major find.
The city of Heracleion was engulfed underwater 1500 years ago. This grand city had been mentioned by the Greek writer Herodotus, the 5th-century BC historian. He had told a wonderful tale of Helen of Troy, who traveled to Heracleion, then a port of 'great wealth', with her Trojan lover, Paris.http://www.sunnyskyz.com/blog/28/An-Ancient-City-Is-Discovered-Underwater-What-They-Found-Will-Change-History-Forever
When French marine archaeologist Franck Goddio stumbled upon some relics, it led them to one of the greatest finds of the 21st century; a city underwater. The discovery took place when Goddio had been in search of Napoleon’s warships from the 1798 Battle of the Nile, when he had been defeated by Nelson in these very waters, but to his surprise, he stumbled upon this magnificent discovery.
The discoveries include the colossal statues of the Egyptian goddess Isis, the god Hapi, and an unidentified Egyptian pharaoh, all preserved in excellent condition by their muddy burial shroud. Along with these 16ft statues there are hundreds of smaller statues of Egyptian gods, among them the figures that guarded the temple where Cleopatra who was inaugurated as Queen of the Nile. Dozens of sarcophagi have also been found, containing the bodies of mummified animals sacrificed to Amun-Gereb, the supreme god of the Egyptians. Many amulets, or religious charms, have been unearthed, too, showing gods such as Isis, Osiris and Horus.
Evidence shows that Heracleion slipped into its watery grave sometime in the 6th or 7th century AD. The discovery of Heracleion will now add depth and detail to our knowledge of the ancient world, because among the discoveries, there are perfectly preserved inscribed pillars decorated with hieroglyphics.
Some excellent photos at link.