The Black Sea has been a part of human history since the first Middle Eastern farmers crossed into Europe, about ten millennia ago. Its shores have been inhabited ever since. Empires fought major naval battles in its waters, ships sank, peoples came and went. Today, hundreds of thousands spend their summer holidays in its bustling resorts, enjoying its beaches. Still, the Black Sea remains an enigma.

It is so little known that facts, rumours and fantasies about its geological past, history, name and outstanding features blend, creating a mythological layer where it is hard to tell truth from imagination.

Durankulak Lake, on the border with Romania, is a haven for birds. Seven thousand years ago, one of its islands housed one of southeastern Europe's earliest farming communities which allegedly pioneered stonemasonry

Let's start with how the Black Sea formed. Scientists agree that until relatively recently, there was no sea at the place where Europe and Asia meet. Instead, there was a lake. Eventually, the lake and the Aegean connected and the Black Sea was born. Traces of this change are still visible today. The Black Sea's salinity is very low, about 17‰, and the great majority of fish and other species that live in it are of Mediterranean origin.

But when the two water basins got linked and how?

According to a hypothesis, about 7,000 years ago, the Aegean Sea violently flew into the lake. The deluge drowned the people who were living along the lake's shores. The survivors remembered the catastrophe and relayed it to later generations. After numerous iterations, it went written down as the story of the Biblical Deluge.

The beautiful Art Nouveau casino in Constanța, Romania, was built in 1910 to serve as a playground for the Romanian elite who frequented this seaside town in summer. After decades of abandonment, when the building was on the verge of collapse, it was renovated and reopened in 2025

Since the 1990s, scientific expeditions have combed the Black Sea's floor sediments in search for evidence. The results are inconclusive. Alternative hypotheses suggest that the prehistoric lake became a sea earlier, about 20,000 years ago, and that the change happened gradually: a slow increase of water levels rather than a dramatic deluge.

The explanations of the sea's dark and menacing name are even more diverse. The earliest name we are aware of dates back to the times when the Greeks were beginning to colonise the sea's shores, in the 9th-8th centuries BC. Initially, they called it Pontos Axeinos, or Inhospitable Sea. The name reflected the sea's treacherous waters and sudden storms, and the newcomers' violent clashes with locals living on its shores. When the Greeks got accustomed to the sea and established viable colonies, they renamed Pontos Axeinos to Pontos Euxeinos, or Hospitable Sea.

The 142-metre grand Potemkin Stairs connect Odessa's centre to the port and are considered a city symbol

Why nations who settled around the Black Sea later opted for its current name remains a mystery. The fact is that the Black Sea is "black" in Bulgarian, Turkish, Romanian, modern Greek, Georgian, Ukrainian and Russian.

The most obvious explanation is either the sea's relatively dark colour or its strong storms and often harsh sailing conditions. Bolder speculations suggest that "euxeinos" has never meant "inhospitable" in ancient Greek. Instead, it meant "black, dark colour" in… Iranian. In ancient times, the claim goes, each cardinal direction was symbolised by a colour and the north was associated with black. As the sea was north of the places inhabited by Greeks, it was called Black.

The toy-like Swallow’s Nest Castle near Yalta, in Russia-occupied Crimea, is small and charming. It was built in 1911 and was used for some time as a restaurant. After the 1917 October Revolution, it became a tourist attraction, which it remains to this day

This "theory" has so many holes it is embarrassing to list them all. A simple check, with two AI language models, for example, shows that the established Old Persian word for something that is black or dark in colour was hamiyā. In Avestan, a sacred Iranian language, it was aspaēna. Did aspaēna transformed to euxeinos? It seems unlikely. And anyways, why would Greeks borrow a name for a sea from the ancient Persians?

Another, even stranger, "theory" explains the Black Sea's name with the fact that  metal objects tend to turn black when they sink down. This is chemically true. However, it is highly unlikely the reason for the sea's name.

This chemical property of Black Sea's waters, however, brings us to the most astonishing fact about it. About 88% of the waters of the Black Sea are virtually dead. Nothing, besides a couple of very determined bacteria species, lives below the surface of 150-200 m. The reason: the sea's depths are full of hydrogen sulphate. There is not enough oxygen here to sustain life.

The crumbling Amra Pier is one of the best-known sights in a lesser-known spot on the Black Sea coast, the resort town of Sukhumi, in the internationally unrecognised Republic of Abkhazia. It seceded from Georgia in the 1990s after a brutal conflict

How did this come to be? It might be, a theory claims, because of the deluge. The sea's rushing waters drowned people, animals and vegetation, and dragged them onto the sea's bottom. There, their decaying remains produced enough hydrogen sulphate to suck out life from most of the Black Sea.

Is the hydrogen sulphate in the Black Sea dangerous? The media regularly fret about some hypothetical catastrophe that could tip the balance and cause an enviromental disaster. According to scientists, however, such scenario is unlikely.

The mysterious dead depths of the Black Sea have given fodder to a range of modern myths. One tells of the "horror" that sailors supposedly feel while crossing the sea. Another is about some Romanian workers who, in the 1990s, stumbled upon the entrance of a mysterious underwater tunnel. The sea is crisscrossed by such tunnels, dug by giants seeking gold, the legend goes.

Ali and Nino kinetic sculpture by Tamara Kvesitadze, in Batumi, Georgia's main seaside town, represents eternal love and universal brotherhood

Unlike these, the saline underflow that runs like a river from the Bosporus to the Black Sea for about 60 km is real. It was discovered in 2010 and behaves like a proper river: it has carved the sea bottom, at places even forming waterfalls and rapids. It is about 35 m deep and about a kilometre wide.

There is hardly a sea without legends about sunken ships loaded with precious objects and hidden treasures. The Black Sea is not exception. Some say that Lisimachus, one of Alexander the Great's generals, hid some gold somewhere around Kaliakra Cape. Valchan Voyvoda, the semi-legendary Bulgarian brigand who in the late 18th and early 19th centuries robbed Ottoman caravans, convoys and rich people, is said to have hidden treasures at numerous places along the shore.

The megapolis now stretches over both sides of the Bosporus Straits, the Black Sea's only outlet to the wider world

And there is the legend of HMS Prince. The ship sank in the Black Sea during the Crimean War, in 1854. Her remains were discovered by Ukrainian scientists in 2010. According to one hypothesis, which has fittingly changed the vessel's name to Black Prince, the ship went down with tonnes of gold. She never reached the sea floor, however. Instead, she was caught in an underwater current. She still rides it, circling around the Black Sea, occasionally popping up on the surface only to go down again.

The legend strongly resembles the story of another ghost ship, the Caleuche, which drifts under the waters of the Chilean archipelago, near Patagonia.