Record low water levels on the Danube — the second longest river in Europe, flowing through ten countries from Germany to the Black Sea — have exposed a remarkable array of submerged history this summer, from dozens of German warships to the foundations of a nearly 1,700-year-old Roman bridge. The extreme drought and heat gripping much of the continent have pushed the river to historically unprecedented lows, stranding boats, disrupting transport, and inadvertently handing researchers and historians an extraordinary window into the past.

In Serbia, the hulls of roughly 200 German warships from World War II have emerged from the riverbed near the surface. The vessels were deliberately scuttled by the German navy as it was being pursued by Soviet forces, with the intention of blocking the river to slow their pursuers. Elsewhere along the Danube, the drought has surfaced a trove of dangerous wartime remnants: in Budapest, Hungary, the wreck of a German Wehrmacht motorcycle was recovered alongside the preserved bodies of two soldiers — their cardboard identity tags still intact — as well as 35 anti-tank mines. In Slovakia, bomb disposal teams carried out a controlled detonation of a 750-kilogram bomb found in the river, while in Cologne, Germany, a 500-kilogram American bomb came to the surface. In the French village of Le Porge, in the Gironde region, more than 400 wartime artillery shells were uncovered following devastating fires.

The falling waters have also revealed ancient history. On the border between Bulgaria and Romania, the stone pillar foundations of a bridge commissioned by the Roman Emperor Constantine the Great have become visible near the village of Gigen in northern Bulgaria. Built in 328 AD and spanning approximately 2.4 kilometres — with more than a kilometre crossing the river itself — the structure was among the longest bridges of classical antiquity. It connected the Roman city of Ulpia Oescus, in present-day Bulgaria, with Sucidava, in modern Romania, and served as a key military and supply corridor. The bridge fell out of use by 367 AD, likely damaged during incursions by Germanic peoples as Roman authority in the region declined. A team from the Regional Historical Museum in Pleven documented the exposed foundations using drone photography. "The nature briefly reveals a monument that is almost always hidden beneath the Danube," said archaeologist Pavel Popov. "We can observe, document and study it on site."

The scenes along the Danube are part of a broader European picture: the Rhine in Germany has also reached historic lows, leaving fishing boats stranded near its banks, while sections of France's Loire riverbed are partially dry. Romania's navy conducted controlled demolitions of submerged rocks to improve water flow, and river cruise traffic in Budapest has come to a halt. For energy generation and freight transport, which rely heavily on navigable rivers, the consequences are severe. For archaeologists and historians, however, the crisis has created fleeting and irreplaceable opportunities to study structures and artefacts that may soon return beneath the water.