A bridge from the Roman Empire peeks out of the Danube

The extremely low water level of the Danube has revealed parts of the foundations of the ancient Bridge of Constantine, giving Bulgarian archaeologists a rare opportunity to document what they describe as one of the most impressive engineering achievements of the Roman Empire.

A series of record-breaking heat waves that hit Europe this summer caused severe drought in parts of the continent, affecting major European rivers, including the Danube and Rhine.

"For archaeologists, moments like this are extremely precious because nature briefly reveals a structure that is hidden under the Danube for most of the time," said Pavel Popov from the Regional History Museum in Pleven.

"It provides us with a rare opportunity to observe, document and study it in its native environment," he added.

Built by Emperor Constantine the Great and opened in 328 AD, the bridge connected the ancient city of Ulpia Aesculus with Sucidava, in what is now Romania. At over two kilometers long, it is considered one of the longest bridges of antiquity, although it was not in use for long. It is believed that most of it was destroyed around 367 AD.

A team of experts from the Pleven Museum conducted aerial photography and documentation of visible bridge remains near the village of Gigen in northern Bulgaria last Tuesday.

Researchers used drones to map and photograph the exposed parts of the structure, determine the position of visible foundations, and assess their condition.

The low water level of the Danube in recent weeks has also revealed parts of history from World War II.

The remains of German warships sunk by retreating Nazi forces in 1944 have resurfaced from a riverbed in Serbia. The ships, located near Prahovo, have been an obstacle to river traffic for decades, and their position has become even more visible due to a prolonged drought and record low water levels.