It's midnight on September 16th, 2017, 60 kilometers off the Bulgarian coast and 2 kilometers beneath the Black Sea’s surface. A remotely operated vehicle  surveys the seabed, transmitting video to researchers  above as it goes. Suddenly, it discerns another ghostly vessel in the gloom. But this is a relic from another age. It's an undoubtedly ancient shipwreck, but its mast, rowing benches, and some  of its upper deck remain eerily intact. It might be an ancient Roman ship,  but its appearance doesn’t quite match. Notably, its splayed rudder blade  more closely resembles those depicted on an even older  Greek vase. To get a definitive answer, the research  team takes three samples from the wreck and radiocarbon dating confirms its ancient origins. The ship is dated to between 350 and 410 BCE. It is, in fact, the oldest intact shipwreck ever found. This ancient Greek vessel traversed the Black Sea’s coasts during the time of Aristotle  and has since rested in its depths, unseen and undisturbed,  for almost 2,500 years. This was just one of 65 shipwrecks a research team discovered at the bottom of the Black Sea between 2015 and 2017. Others date from the Roman, Byzantine, and Ottoman empires. And despite the centuries, they’ve all survived in remarkable condition. So, why does the Black Sea contain so many well-preserved shipwrecks? In prehistoric times, the land surrounding the Black Sea hosted early human settlements. Eventually, it became a hub for trade, battle, and empire-building because of its strategic position between eastern and western  Eurasian civilizations. For thousands of years, it was traversed by merchants, pirates, and warriors. And with sustained seafaring activity came inevitable losses. But unlike other bodies of water  in the region, the Black Sea is a particularly deep, semi-enclosed basin. Seasonal changes usually cause the layers  within a contained body of water to mix together,  oxygenating the water. But because the Black Sea is fed  with fresh water from European rivers, and saltwater from the Mediterranean Sea, it contains two distinct layers. The denser saltwater flows beneath the freshwater, where it remains permanently, making the Black Sea the world’s largest meromictic— or un-mixing— basin. Oxygen doesn’t reach  its lower, saltier zone, which creates the ideal environment for preservation, and is why the Black Sea has been called “the world’s biggest pickle jar.” In other bodies of water, marine organisms decompose materials over time. Had the ancient Greek ship sunk  in the Mediterranean, for example, there would likely be no organic material  left today. But in the depths of the Black Sea, only anaerobic bacteria— those that don’t require oxygen— can survive. This is why ancient ships can still be found carrying their original cargo, with carvings in their wood, and their rigging still assembled. Among the recent findings was  a medieval Italian merchant ship, likely from around the time Italy had  a virtual monopoly over Black Sea trade. Venetian traveler Marco Polo would’ve probably been familiar with this kind of ship. Although vessels like this one helped to modernize Europe, contemporary scholars had never before seen such a complete example. And it was largely intact— a ship’s boat still lying on its deck, even though some seven centuries had passed. Many of the 65 ships that were  recently uncovered have retained their original forms. But while there are far fewer degradative  forces at play in the Black Sea’s depths, anaerobic bacteria do gradually weaken organic materials. When researchers lifted a plank from the ancient Greek wreck for dating, it broke under its own weight. While the ships are exceptionally well-preserved, they're also fragile. This makes it impossible to bring them to the surface intact. Scientists may carefully remove and study  select objects from the wreckages. But the sunken ships will remain protected where they are, perhaps among thousands of others— deep beneath us, suspended in time,  at the bottom of the Black Sea.