Water levels in rivers across Europe are reaching astonishing lows lately as a record heatwave continues to bake much of the continent.

Images captured by the European Union’s Copernicus Sentinel-2 satellite revealed the extraordinary extent of the drought, which is clearly desiccating Europe’s major waterways. Water levels in one of those rivers, the Danube, have become so low that ancient ruins are beginning to surface for the first time in centuries.

As Reuters reported, the portion of the Danube that flows through Bulgaria has slowed to a mere trickle, revealing foundations of the Constantine Bridge, a nearly 1,700 year-old structure that was opened for business back during the rule of Roman Emperor Constantine the Great in the year 328 AD.

Though the bridge is believed to have been destroyed just a few decades after it was finished, researchers regard it as among the longest bridges engineered by the Roman Empire, a marvel of ancient engineering. Though receding water levels come with plenty of downsides, Pavel Popov, a Bulgarian archeologist with the Pleven Regional Historical Museum told Reuters that the droughts do offer a unique opportunity to study the ancient wonder.

“For archaeologists, these moments are ​extremely valuable because nature briefly reveals an object that ​is hidden beneath the Danube for most of the time,” Popov explained. “It gives us ​a rare opportunity to observe, document and study it ​in its real environment.”

After the ruins surfaced, Reuters reports that local researchers used drones to survey the exposed ruins, with the low water levels offering a chance to trace the bridge’s physical footprint and evaluate the condition of the foundation materials.

Numerous other treasures have surfaced across the Danube, like the remains of a mammoth tusk in the Bulgarian village of Ryahovo, and a sunken Nazi warship near the Croatian town of Opatovac.

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