Low Danube waters in Bulgaria expose foundations of famous Roman bridge

Exceptionally low water levels on the Danube River this summer have once again peeled back layers of history, this time revealing the long-submerged foundations of one of the Roman Empire’s most ambitious engineering projects on the territory of northern Bulgaria.

A succession of intense heatwaves and prolonged drought across Europe has left the continent’s second-longest river at critically low levels, exposing sandbanks, rocks, and long-hidden archaeological treasures. Near the village of Gigen in northern Bulgaria, the receding waters have brought into view portions of the stone foundations of Constantine’s Bridge (also known as the Constantine Bridge or Pons per Danuvium Ductus), giving archaeologists a rare window to study a structure that has remained largely underwater for centuries.

“For archaeologists, these moments are extremely valuable because nature briefly reveals an object that is hidden beneath the Danube for most of the time,” said Pavel Popov of the Regional Historical Museum in Pleven. “It gives us a rare opportunity to observe, document and study it in its real environment.” Last week, a team from the museum used drones to photograph and map the visible remains, carefully tracing the line of the foundations and assessing their condition.

Low Danube water levels in Bulgaria expose Roman-era bridge https://t.co/GDnRXKOhPe https://t.co/GDnRXKOhPe
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An engineering marvel of the late Roman Empire

Commissioned by Emperor Constantine the Great and inaugurated on or around 5 July 328 AD in his presence, the bridge linked the major Roman colony of Ulpia Oescus (near modern Gigen, Bulgaria) on the southern bank with the fortress of Sucidava (near present-day Corabia, Romania) on the northern bank. At roughly 2,437 metres (about 2.4 km or 1.5 miles) in total length – of which approximately 1,137 metres spanned the riverbed itself – it is widely regarded as the longest river bridge of antiquity and one of the longest bridges built anywhere in the ancient world.

🌉 Constantine’s Bridge over the Danube: A Roman Marvel Lost to Time 🛠️⚔️
In 328 AD, Emperor Constantine the Great inaugurated one of the most ambitious infrastructure projects of Late Antiquity: a massive bridge over the Danube River. Spanning an incredible 2,434 meters, the… pic.twitter.com/0Cc406ntL2
— MindVoyager (@Karol1669024) July 4, 2025

The structure featured solid masonry piers supporting a wooden superstructure and deck. It measured about 5.7 metres (19 feet) in width and rose roughly 10 metres (33 feet) above the water. Designers drew inspiration from the earlier and celebrated Trajan’s Bridge further upstream, employing similar techniques adapted for the site’s conditions. The bridge served primarily military purposes, enabling rapid troop movements across the Danube as Rome sought to reassert control over territories north of the river and counter threats from Goths, Sarmatians, and other groups. In 332 AD, for example, Constantine’s son and co-emperor Constantine II used it to lead a large army against barbarian forces.

Despite its impressive scale, the bridge had a short operational life. It is believed to have fallen out of use or been largely destroyed by around AD 367, when Emperor Valens was forced to cross the Danube via a temporary pontoon bridge during a campaign against the Goths. Over the centuries, the wooden elements vanished and the stone foundations settled into the riverbed, only occasionally becoming visible during extreme low-water events.

A summer of revelations along the Danube

The exposure of Constantine’s Bridge is the latest in a series of striking finds uncovered by the same drought. Just days earlier, in late July 2026, the remains of a woolly mammoth emerged from the riverbed near the village of Ryahovo in northeastern Bulgaria, not far from the city of Ruse. A local resident spotted the large bones; specialists from the Regional History Museum in Ruse identified a lower jaw, two tusks, a possible rib, and additional fragments. Experts believe the animal was a woolly mammoth (Mammuthus primigenius), potentially a young adult that could have stood nearly five metres tall and weighed several tonnes. The remains are being carefully conserved and studied to determine their precise age – likely several thousand years old – and origin. Prehistoric animal fossils are not uncommon in the region, and the museum already houses other mammoth specimens.

Low Danube waters reveal Ice Age mammoth remains in Bulgaria

Farther upstream, near the Serbian port of Prahovo on the Serbia–Romania border, the same low water levels have once again brought into view the rusting hulks of dozens of World War II-era German warships. In September 1944, as Soviet forces advanced, Nazi Germany’s Black Sea fleet deliberately scuttled up to 200 vessels in a zigzag pattern across the Danube to impede the Red Army’s progress. Many of the wrecks – some still containing unexploded munitions, shells, and mines – rest on the riverbed. At least 20 have become clearly visible this summer, narrowing the navigable channel and posing ongoing hazards. Similar exposures occurred during severe droughts in 2022 and 2024, prompting Serbian authorities, with European Union and European Investment Bank support, to begin carefully removing some of the most obstructive wrecks.

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These discoveries highlight both the scientific value of extreme low-water events and the broader impacts of climate-driven drought on Europe’s major waterways. While the receding Danube has disrupted shipping, tourism, and even energy production in places, it has also offered fleeting opportunities for researchers to document and study artefacts that are normally inaccessible. For the Constantine Bridge, the current window may close as soon as water levels recover, underscoring the urgency of the recent drone surveys and documentation efforts near Gigen.

Caption: Artist view of the Constantine bridge