How archaeologists found a sunken Roman city off Egypt

HostIt's strange to think that even now, with satellites and maps for everything, we can still lose track of a whole city. Not just a building or a small house, but a massive trade hub with huge temples and thousands of people. How does a place that big just disappear?

GuestWell, for about a thousand years, it was basically a ghost story. People read about it in old books, but nobody could find it. It turns out it was just a few miles off the coast of Egypt, sitting under the waves.

HostIf it's that close to the shore, how did it stay hidden for so long? You would think a diver or a fisherman would've bumped into a statue or something by now.

GuestThe water there's not always clear and blue. Near the mouth of the Nile River, it's very murky because of all the mud and sand the river carries into the sea. The city didn't just sink into the water; it sank into the floor of the sea. By the time the search started, it was covered in thick layers of clay. You could swim right over it and see nothing but a flat, gray bottom.

HostSo you can't see it with your eyes. How do you start looking for a needle in a haystack when the haystack is at the bottom of the ocean?

GuestYou stop using your eyes and start using magnets. The team spent years towing magnetic tools behind boats. These tools map the pull of the sea floor. Most of the bottom is just mud, which has a very steady, boring pull. But when you hit a huge block of stone or a pile of iron, the needle jumps. They mapped every little bump over miles of water until they saw shapes that didn't look like nature. They saw straight lines and right angles.

HostI don't know if I buy that a magnet can tell the difference between a rock and a temple. Rocks are everywhere down there.

GuestThat's the thing. This part of the bay shouldn't have huge rocks. It's all soft mud. So when the tools showed these massive, heavy clusters in specific patterns, they knew it had to be man-made. When they finally sent divers down to dig through the mud, they hit stone. They cleared off the grime and found these giant statues of gods and kings, some of them fifteen feet tall, still standing upright or lying on their backs like they were just sleeping.

HostThat sounds like a movie, but it's hard to wrap my head around a city just sliding into the water. Cities are heavy. They're built on solid ground. Did the sea level just rise really fast?

GuestIt was more like the ground gave up. This city, which was called Thonis-Heracleion, was built on a group of islands in the mouth of the Nile. The soil was mostly clay and sand. If you have ever stood at the edge of the beach and wiggled your toes in the wet sand until you sink, you have seen a tiny version of what happened. A series of floods and maybe an earthquake hit, and it caused the ground to turn to liquid.

HostThe ground turned to liquid? That sounds like a disaster film.

GuestIt's a real thing that happens to wet soil under pressure. The water between the grains of sand gets squeezed. The soil stops acting like a solid and starts acting like a soup. The weight of those massive stone temples was too much. The islands literally folded and slumped into the sea. In some places, the ground dropped twenty or thirty feet in an instant. The buildings didn't just fall over; they were swallowed.

HostIf it happened that fast, there must be a lot of stuff left behind. It's not like they had time to pack their bags.

GuestThat's why it's such a gold mine. It's a time capsule. Because the mud covered everything so quickly, it kept oxygen away. Oxygen is what makes things rot. When the divers dug, they found wooden boats that were still held together. They found tiny gold earrings, bronze weights for scales, and even baskets of fruit that had turned to charcoal but still kept their shape. You can see the daily life of a sailor or a merchant from two thousand years ago just lying there.

HostIt's wild that a place that important can just vanish from the map. Was it a big deal back then, or was it already on its way out?

GuestIt was the front door to Egypt. Every Greek ship that wanted to trade had to stop there to pay taxes and move their goods onto smaller river boats. It was a place of huge wealth. But as nearby cities grew, this one became less important. Then the ground started shifting, and by the end of the eighth century, the last bits of it were gone. The sea just moved in and took over.

HostI'm still stuck on the statues. You mentioned they were huge. How do you even get something that big out of the mud without it snapping in half?

GuestIt took months of planning for each one. They used massive cranes on ships and built special slings to cradle the stone. They had to be very careful because, even though the stone is tough, a thousand years in salt water can make it weak. Watching those faces rise out of the water for the first time in a thousand years must have been incredible. They looked brand new because the mud had protected them from the currents.

HostIt makes me wonder what else is sitting just a few miles off a coast somewhere else, hidden by a bit of sand and time.

GuestThey found a tall stone slab with laws about taxes carved into it, still standing perfectly upright in the spot where it was placed twenty-four hundred years ago.

HostThe maps we have now seem so finished, but those pillars in the mud remind us that a whole world can still be hiding just a few miles from the shore.