The History of the Mediterranean Sea: Geology, Facts, and Human Legacy

The Mediterranean Sea is one of the largest seas on Earth, covering roughly three million square kilometres when its dependent seas — the Marmara, Black and Azov seas — are included. It borders three continents, hosted many of the ancient civilizations of the Mediterranean Basin, and its geological history stretches back millions of years, encompassing a near-total drying out and one of the most catastrophic floods our planet has ever witnessed. This article traces that history, from the closure of the ancient Tethys Ocean to the Byzantine Empire. The Mediterranean Sea is one of the largest seas on our planet.

The history of the Mediterranean Sea

The Mediterranean Sea has a long and eventful history that modern science reconstructs far beyond the short span of human memory. Within living memory the sea has behaved calmly: winter brought fierce storms, summer invited bathers into warm, gentle waters over golden sand beaches, and occasional volcanic eruptions or local rises and falls of the seabed left the coastline essentially unchanged. Yet geologists have shown that over millions of years the Mediterranean Sea repeatedly filled and emptied, disappeared into desert and was reborn as an ocean broke through to fill it again.

Today science is no longer content with the brief memory available to humanity; it investigates ever more closely the origin of the Universe (more: Scientists on the rotation of the Earth) in which we live, the planet we inhabit, and the seas we sail — the Mediterranean Sea among them.

General characteristics: area and boundaries of the sea

The Mediterranean Sea washes three parts of the world — Europe, Asia and Africa — and connects to the Atlantic Ocean through the narrow Strait of Gibraltar in the west and to the Black Sea through the Bosporus and the Sea of Marmara in the east. The surrounding countries range from Spain, Morocco and Egypt to Greece, Turkey and the coasts of the Levant. Its major islands include Sicily and Sardinia, while the Suez Canal links it artificially to the Red Sea. The sea's various names in multiple languages all descend from Latin Mare Mediterraneum, "the sea in the middle of the land."

Depth of the Mediterranean Sea

The Mediterranean Sea is among the deepest seas on Earth: the maximum depth of the Mediterranean Sea reaches 4,404 metres, in the Calypso Deep of the Ionian Sea. The average depth is roughly 1,500 metres, and the basin is divided into a western and an eastern deep by the shallow sill between Sicily and Tunisia. These basin depth measurements reflect a complex floor shaped by subsiding abyssal plains, submarine ridges and the deep canyons carved into it during earlier dry phases.

Rivers flowing into the Mediterranean Sea

Several of the most famous rivers of the Old World empty into the Mediterranean Sea: the Nile, the Danube, the Dnieper, the Don, the Po and the Rhône. The Nile River, draining much of northeastern Africa, delivers its waters at the great delta in Egypt, while the Rhône reaches the sea on the southern coast of France. This freshwater inflow is nonetheless far smaller than the volume evaporated each year, which is why the Mediterranean depends on the Atlantic Ocean to stay full.

Climate and water temperature

The Mediterranean Sea gives its name to the Mediterranean climate — hot, dry summers and mild, wetter winters — that characterises its coastal regions. Surface water temperature swings from around 12–15 °C in winter in the north to 25 °C or more in summer along much of the coast, warmer still in the eastern basin. Because the sea loses about one and a half thousand cubic kilometres of water to evaporation every year, more than its rivers and rainfall supply, water is drawn in continuously from the Atlantic through the Strait of Gibraltar, keeping the Mediterranean saltier and warmer than the open ocean.

How the Mediterranean Sea formed

The Mediterranean Sea is the remnant of a far older ocean, the Tethys Ocean, that once separated the northern and southern landmasses of the supercontinent Pangea. As Pangea broke apart during the Mesozoic and seafloor spreading opened new ocean basins, the Tethys began to close, squeezed between the drifting African Plate and Eurasian Plate. The Mediterranean basin geology we see today records the long, slow narrowing of that ancient sea into the enclosed basin of the present.

Alpine orogeny and the Mesozoic origins of the basin

The Alpine Orogeny, the mountain-building episode that raised the Alps, Pyrenees, Atlas and Hellenic ranges, is inseparable from the closure of the Tethys Ocean and the formation of the Mediterranean Sea. During the Miocene the collision between the African and Eurasian plates crumpled the intervening crust, throwing up orogenic belts around the shrinking sea. The Mediterranean therefore sits in a mosaic of geomorphological settings — stable margins where old continental crust is quiet, convergent margins where plates collide, and extensional margins where the crust is being pulled apart.

Plate tectonics: the Calabrian and Hellenic arcs

The subduction of the African Plate beneath the Eurasian Plate drives the tectonics of the Central Mediterranean and shapes two great curved features, the Calabrian Arc and the Hellenic Arc. As the African Plate sinks along the Hellenic Trench, the overriding plate stretches and volcanic activity erupts behind the arc — the volcanism of Central Mediterranean islands and mainland volcanoes is a direct product of this process. Geologists recognise four major extensional phases in the Central Mediterranean that opened back-arc basins as the subduction zone rolled backwards over time.

Between these arcs lies the Mediterranean Ridge, a broad convergent margin feature built from sediment scraped off the descending plate. The Ionian Sea contains the deeply subsided Ionian Abyssal Plain, one of the flattest and lowest parts of the whole basin, bordered by rises such as the Sirte Rise off North Africa.

Geology of the Adriatic Sea

The Adriatic Sea occupies a zone of compressional deformation where the small Adriatic block pushes against the surrounding orogenic belts. This shortening folds and thrusts the crust, feeding the ongoing growth of the mountains that ring the Adriatic and making the region seismically active. Its geology contrasts with the deep abyssal plains further south, since much of the Adriatic is comparatively shallow shelf sea overlying thickened continental crust.

The Aegean Sea: extension and subduction

The Aegean Sea, between Greece and Turkey, is a classic example of extension above a subduction zone: as the African Plate dives along the Hellenic Arc, the overriding Aegean crust is stretched and thinned, dropping blocks that form the sea's many islands and basins. This combination of subduction features and active extension makes the Aegean one of the fastest-deforming regions in the Mediterranean, prone to earthquakes and volcanism alike.

The Mediterranean six million years ago

About six million years ago the Mediterranean Sea nearly ceased to exist, an episode geologists now call the Messinian salinity crisis. Cut off from the Atlantic Ocean, the sea evaporated faster than its rivers could replenish it, its level dropped catastrophically and its salinity soared until most marine life perished. Where the familiar sea now lies there would then have stretched a deep, dead desert, in places sinking, by some estimates, more than two kilometres below the level of the ocean.

The discovery of Charles Lyell

Nearly two hundred years ago, in 1833, the English geologist Charles Lyell studied the history of the Mediterranean Sea and noticed a striking break in the fossil record. He observed that around six million years ago the marine fauna of the Mediterranean — which had carried mixed features of Atlantic and Indian Ocean life, because the sea originally had outlets to both great oceans — largely died out. That extinction marked the moment the Mediterranean lost its connection to the world ocean.

The drying of the sea and the rise in salinity

Living conditions in the waters of the sea became unbearable: the Mediterranean grew shallow rapidly, and the salinity of its waters rose sharply. This could happen only one way — external waters, the waters of the ocean, stopped flowing into the basin, and the sea was left on a starvation ration. Had maps been drawn in those times, a dead desert would have occupied the place of the famous sea.

It would have been a very peculiar desert. A few lakes remained within it, fed by the great rivers, but despite the constant inflow of fresh water these lakes were so briny that almost nothing lived in them. Only a handful of dwarf species of molluscs and snails, able to endure the ultra-high salinity of their environment, survived. Thick layers of salt and gypsum precipitated across the drying floor — the evaporite deposits that today are the geological signature of the Messinian salinity crisis.

Ancient canyons on the sea floor

The desert floor of the Mediterranean was cut by deep canyons, down which the great rivers that still empty into it today drained toward the remaining small salt lakes. As the base level fell by kilometres, each river sliced far below its present bed, leaving buried gorges that borehole surveys would later reveal.

Borehole and seismic survey data

As early as the end of the 19th century, during a search for groundwater, the ancient channel of the Rhône was discovered where it meets the Mediterranean on the southern coast of France; in the delta it was found buried under sediments about a kilometre deep. Later drilling confirmed how deeply the rivers had cut during the crisis.

The Russian geologist I. S. Chumakov, working on the construction of the Aswan dam, carried out boreholes and found beneath the bed of the Nile a narrow, deep gorge cutting the granite bedrock of the continent to two hundred metres below the present sea level — and Aswan lies more than a thousand kilometres from the mouth of the great river. In the modern Nile delta, boreholes three hundred metres deep failed to reach the bottom of the ancient canyon. Chumakov believes the floor there descends to about one and a half kilometres below the modern sea level. Similar narrow gorge-canyons have been found across Algeria, Syria, Israel and other countries around the present Mediterranean, all formed in the age when the Mediterranean Sea did not exist. Seismic surveys across the whole basin have since traced the salt layers and buried valleys that corroborate this reconstruction.

The catastrophic flooding of the basin

The Messinian salinity crisis ended abruptly when Atlantic water breached the barrier at Gibraltar and refilled the desiccated basin in an event known as the Zanclean flood, or the Pliocene Revolution. About five and a half million years ago a mighty upheaval broke the mountain chain that had separated the Atlantic Ocean from the Mediterranean and opened the Strait of Gibraltar. Where the two water bodies joined, a colossal waterfall arose, with a total drop reaching two to three kilometres and a discharge exceeding the flow of Niagara Falls roughly a thousandfold.

The breach of Atlantic waters through Gibraltar

The creation of the Strait of Gibraltar reconnected the Mediterranean Basin to the Atlantic Ocean and let the marine Pliocene re-establish itself, restoring normal sea life within a geologically brief span. Rather than a single quiet trickle, the refilling appears to have accelerated into a torrent that carved a channel through the sill between the Betic mountain range of Spain and the Rif mountain range of Morocco, leaving visible seabed scarring that survives beneath the sediments today. Quaternary transgressive raised terraces along Mediterranean coasts record later, smaller oscillations of sea level after the basin was full again.

Computer modeling of the prehistoric flood

Modern computer modeling of the Zanclean flood has put striking numbers on the event. Work led by Daniel Garcia-Castellanos of the Institute of Earth Science Jaume Almera, with colleagues including Roger Pibernat, and published in the journal Nature, concluded that the Mediterranean Sea may have refilled in as little as a few months to two years, with sea level rising by more than ten metres a day at the peak. Their models describe water flow velocities and forces capable of eroding an incision hundreds of metres deep through the Gibraltar sill, discharging up to around a hundred million cubic metres per second — a scale unmatched by any river on Earth, dwarfing even the Amazon River. This timeline of the deluge frames it as one of the largest floods in the planet's history.

The history of the Mediterranean Sea and its structure

Scientists who studied the history and structure of the Mediterranean Sea established that over millions of years the strait connecting the sea to the ocean opened and closed repeatedly. The drying of the sea proceeded quickly: it required only about a thousand years, and the subsequent refilling by ocean waters probably took no longer. Each time, at the junction of the water bodies, a powerful waterfall arose in which the total height of the falling water reached two to three kilometres and the volume exceeded the flow of Niagara Falls about a thousandfold.

Cycles of opening and closing of the strait

Twentieth-century engineers even drew up a project to build a giant hydroelectric power station in the Strait of Gibraltar, one that would run on the difference in water levels between the Atlantic Ocean and the Mediterranean Sea. To create that difference, the sea was to be somewhat "dried out" by restricting the inflow of Atlantic waters — feasible because about one and a half thousand cubic kilometres of water evaporate from its surface each year. Once the level difference reached about fifty metres, powerful turbines would be switched on. Beyond the enormous power such a station would supply, the plan promised to expose large tracts of land that could be planted with vineyards and orchards.

This project, however, is unlikely ever to be carried out: it could trigger changes in the climate of all of Europe that no benefit could offset, and science cannot yet foresee those consequences in advance.

In those distant times the Mediterranean Sea could also have received water from another source — and not the Indian Ocean. To the east and north lay a gigantic lake-sea that entirely overlay the present Black, Azov, Caspian and Aral seas. The waters of that vast lake-sea would surely have poured into the then almost waterless Mediterranean depression, but their path was blocked by the Carpathians, young mountains at the time. In all likelihood the waters of that lake-sea were fresh, or only slightly brackish.

Mediterranean waters in the Black Sea basin

The Black Sea was practically fresh in those years, and remained so even after its outline approached the modern one about three million years ago. The salty waters of the Mediterranean Sea managed to penetrate the basin of the Black Sea only around 370 thousand years ago, and their inflow ceased 230 thousand years ago, when fresh movements of the Earth's crust in the region of the straits of the Sea of Marmara closed the passage.

The Black Sea then subsisted only on the waters of its inflowing rivers and quickly began to freshen. The first phase of the Black Sea's salinisation was discovered by the Rostov scientist B. L. Solovyov. Near the town of Sukhumi he found the fossilised remains of salt-loving Mediterranean molluscs and was able to date them fairly precisely — a discovery made in the 1970s. After this the Black Sea went through a whole series of successive salinisations and freshenings.

The next salinisation occurred about 175 thousand years ago, then 100 thousand years ago, then 52 thousand years ago. Thirty-eight thousand years ago the sea again became fresh and stayed so for several tens of thousands of years. Only 7 thousand years ago, when the doors of the Sea of Marmara opened once more, did the latest salinisation of the Black Sea begin — the one that continues to this day.

It would be within human power today to cut off the Black Sea basin from the inflow of salty Mediterranean water and, by building a dam, to erect a fairly powerful power station on the resulting water-level difference. But should such a dam be built? How can one calculate the climatic changes its construction would bring? Shallow waters would be exposed, a large part of the Sea of Azov would dry up, leaving only a freshwater lake fed by the Don. What would become of the famous resorts of Crimea and the Caucasus coast, and of the well-equipped ports and quays? Such a dam and power station hardly hold more arguments in favour than against.

Ancient civilizations and cultures of the Mediterranean

On the shores of the Mediterranean Sea flourished some of the greatest cultures and civilizations in history, which is why the sea holds such historical significance to Western civilization. Early human habitation clustered around its coasts and islands, drawn by mild climate, fisheries and easy sea travel. Over millennia the Mediterranean became the great highway of trade routes and commerce that carried goods, ideas and peoples between three continents, and no other sea can be compared with it for its role in shaping the ancient world.

Civilizations of the Mediterranean Basin

The Mediterranean Basin was the cradle of a succession of ancient civilizations. The Phoenicians, master seafarers, spread trade colonies and their alphabet along the coasts; Egypt built an enduring state on the Nile; and Greece scattered city-states across the Aegean Sea and beyond. The Roman Empire eventually brought the entire coastline under a single power, dominating the sea so completely that Romans called it Mare Nostrum — "our sea." Under the first emperor, Augustus, this Roman control over the whole Mediterranean reached its height, unifying commerce and culture around the basin.

Ancient philosophers and scientists

The Mediterranean world was also the setting for a remarkable flowering of intellectual life. Greek philosophers and scientists such as Plato and Aristotle laid foundations for Western thought, while the Ancient Library of Alexandria in Egypt gathered the learning of the age into one institution. Rulers before them, such as the Persian king Darius I, had already linked the seas by ambitious engineering, and the exchange of knowledge around the Mediterranean created a shared intellectual tradition that later ages would build upon.

The Byzantine Empire and the medieval period

After the western Roman Empire fell, the Byzantine Empire carried Mediterranean civilization through the medieval period from its capital on the Bosporus. Islamic expansion then brought Arab rule to much of the southern and western shores, and during the Islamic Golden Age centres such as Al-Andalus in Spain became crossroads of scholarship, where figures like Ibn Sina transmitted and advanced science and medieval and Renaissance philosophy. Islamic universities and madrasahs — among them the University of Al-Karaouine in Morocco and Al-Azhar University in Cairo, both among the oldest universities in the world — flourished alongside the later Christian University of Bologna, the origin of European universities.

This long tradition of learning and cross-cultural interaction still shapes higher education around the sea. University networks in the Mediterranean, such as the Community of Mediterranean Universities, the Council of Mediterranean Universities and the Black Sea Universities Network, foster cooperation and student and academic mobility, while European Union programmes like ERASMUS move hundreds of thousands of students across borders each year. Institutions such as Istanbul University and Istanbul Technical University, and scholars including Gülsün Sağlamer, continue the region's centuries-old role as a meeting place of cultures, with organisations like UNESCO and OpenEdition helping preserve and share its heritage.

Conclusion

The age and history of the Mediterranean Sea are measured in millions of years. From the closure of the Tethys Ocean and the mountain-building of the Alpine Orogeny, through the near-total drying of the Messinian salinity crisis and the astonishing Zanclean flood that refilled it, to the rise of the Phoenicians, the Roman Empire, the Byzantine Empire and the great universities of the Islamic and European worlds, the Mediterranean has been both a geological wonder and a cradle of civilization. Its restless past — of straits opening and closing, of basins draining and refilling — reminds us that even the most familiar sea has a story far longer and stranger than human memory alone could tell.