The world's earliest known navigational tool used by Vasco da Gama's fleet was discovered in a shipwreck off the Oman coast, NPR reports. Called a marine astrolabe, it's believed to date from 1495 to 1500. Unlike the Game of Thrones intro astrolabe, sailors used this one to figure out where they were on the high seas. It was found in the wreck of the Esmeralda, part of the Portuguese explorer's armada. Da Gama, who discovered the first sea route from Europe to India, was returning home from his second trip there when he left some ships in the Indian Ocean to "disrupt maritime trade," meaning pillage. Several of the ships sank during a fierce storm in 1503. The Esmeralda was discovered in 1998. Since excavations began in 2014, University of Warwick researchers have recovered 2,800 artifacts, the jewel of the cache being the astrolabe, a bronze disc measuring 7 inches in diameter.
Emblems depict the Portuguese coat of arms and the personal stamp of King Dom Manuel I. "It was like nothing else we had seen, and I immediately knew it was something very important because you could see it had these two emblems on it," team leader David Mearns of Blue Water Recoveries tells the BBC. "It's a great privilege to find something so rare, something so historically important." At first, the team wasn't 100% sure it was an astrolabe, but laser scans revealed navigational marks around the edges every 5 degrees, which sailors would have used to calculate their location by measuring the sun's position above the horizon at noon. (A ship that sank in 1BC may hold priceless treasures.)