# The Sea That Vanished

*Marius Comper · 8 September 2026 · [Interactive edition](https://mariuscomper.uk/marea-care-a-disparut/en/) · [Română](https://mariuscomper.uk/marea-care-a-disparut/index.md)*

For more than twenty million years, most of the ground Romania stands on was sea floor. Paratethys, the sea shut in between the Alps and Central Asia, at one point became the largest lake in Earth's history: 2.8 million square kilometres, more than today's Mediterranean. At its highest level, 81.5% of the country's present territory lies under water. The interactive edition puts the sea back over today's country, with a time slider and every county cut along the maps.

## Five moments

| Moment | When | Map source | Of today's Romania, under water |
| --- | --- | --- | --- |
| Badenian sea | 17–13 million years ago | NordNordWest, after the Lower Austrian State Museum, 2005 | 78.8% (187,148 km²) |
| Giant lake, maximum level | 11.6–9.75 million years ago | Palcu et al. 2021, fig. 1 | 81.5% (193,442 km²) |
| Lake Pannon | 11 million years ago | NordNordWest, after the same museum | 50.6% (120,098 km²) |
| Great Khersonian Drying | 8.3–7.65 million years ago | Palcu et al. 2021, fig. 1 | 9.2% (21,867 km²) |
| Today | now | Natural Earth | 0.1% |

Area of today's Romania: 237,432 km² (geoBoundaries), in an equal-area projection.

## How a sea closes

Some 34 million years ago, at the start of the Oligocene, the mountain chains rising from the collision of Africa with Europe cut the northern part of the old Tethys Ocean off from the rest. The water left north of the Alps, the Dinarides and Anatolia got the name Paratethys: a wide, shallow sea stretching from the Vienna Basin to beyond the Aral Sea.

Between 17 and 13 million years ago, in the Badenian, the water was as salty as the ocean and connected to the Mediterranean. It covered the Pannonian Plain, Transylvania, Moldavia and the Romanian Plain; of Romania's present territory, only the Carpathians, Dobrogea and part of the north stayed dry. Then, 13.81 million years ago, the link to the ocean tightened and the sea began to evaporate faster than it filled. Until 13.32 million years ago, salt precipitated on the floor of the basins in Transylvania, in front of the Carpathians and in southern Poland, in layers hundreds of metres thick. The Badenian salinity crisis is why Romania has Praid, Turda, Ocna Mureș, Sovata, Dej, Slănic, Ocnele Mari and Cacica.

Around 11.6 million years ago the last straits closed and Paratethys was left a lake: 2.8 million square kilometres, slightly larger than today's Mediterranean, holding 1.77 million cubic kilometres of water, more than a third of the Mediterranean's volume, according to Dan Palcu (GeoEcoMar, University of Bucharest) and his colleagues. Its water carried 12–14 grams of salt per litre, about a third of the ocean's and less than today's Black Sea, at 17–18 grams. On the reconstruction of the maximum level, the lake covers 81.5% of present-day Romania. Eighteen counties lie entirely under water: Argeș, Bacău, Botoșani, Brăila, Buzău, Constanța, Covasna, Dâmbovița, Gorj, Ialomița, Iași, Ilfov, Mehedinți, Bucharest, Prahova, Vâlcea, Vaslui and Vrancea. The Carpathians stay above, and so does a piece each of Bihor (32%), Sibiu (36%), Suceava (36%) and Alba (41%).

The smallest baleen whale known, *Cetotherium riabinini*, lived in this lake; the skeleton found in Ukraine is about three metres long.

## The lake that emptied by three quarters

Between 11 and 7.5 million years ago, Paratethys went through four hydrological crises, dated by Palcu and his colleagues on the cliff at Cape Panagia, on the Taman Peninsula. The first brought the water down by about 230 metres. The last, the Great Khersonian Drying, began 8.3 million years ago, worsened between 7.9 and 7.65 million years ago, and lowered the level by more than 250 metres. The lake lost about 70% of its surface and a third of its volume; up to 1.75 million square kilometres of lake floor were exposed. The remaining water gathered into a salt lake in the Black Sea basin, at 28–33 grams of salt per litre according to the model, and into a few freshened lakes at the margins. Then, 7.65 million years ago, the Maeotian transgression refilled the basins, but the lake was never whole again.

## Where the sea still shows

The Vienna and Pannonian basins broke away from the rest of the sea 11.6 million years ago; the Transylvanian Basin followed 11.3 million years ago, a date obtained on volcanic ash at Oarba de Mureș. That is why the two maps from roughly 11 million years ago contradict each other about Transylvania: the Austrian map shows it dry, Palcu's reconstruction keeps it under water. Lake Pannon was filled by deltas advancing through it by about 67 kilometres every million years; its own fauna disappeared around 4 million years ago. The Dacian Basin, the water in front of the Carpathians, filled with sediment in the late Pliocene and early Pleistocene. The Black Sea and the Caspian are what is left of Paratethys.

The traces: the salt at Praid and Slănic; the concretions in the Buzău sands (the Ulmet "old women", Bozioru commune), grown in the sands of a delta that flowed into the lake; the oil and gas of the Romanian Plain and Transylvania; the Romanian Plain itself, the floor of a basin filled to the brim.

## Method

The maps were extracted from figure 1 of "Late Miocene megalake regressions in Eurasia" (Palcu et al., *Scientific Reports*, 2021, CC BY 4.0), georeferenced on its own meridians, its 40° parallel and the modern coastlines drawn on it (mean residual 9 pixels, roughly 35 kilometres), and from NordNordWest's maps on Wikimedia Commons for 17–13 and 11 million years ago (CC BY-SA 3.0 de), fitted on the borders drawn on them (mean residual 7 kilometres). Today's borders, coasts and rivers are from Natural Earth; the outlines of Romania and its counties are from geoBoundaries. Areas are computed in EPSG:3035 after a 7-kilometre smoothing of the extracted shorelines. Figures in the text come from Palcu et al. 2021; de Leeuw et al. 2010 and 2018; Vasiliev et al. 2010; Magyar et al. 2013; Jipa and Olariu 2009; Gol'din et al. 2014; Encyclopaedia Britannica; Dan Palcu's interview with Digi24, December 2023.