[Pavel Popov/Pleven Regional History Museum/Handout via Reuters]

Exceptionally low water levels on the Danube have exposed parts of the foundations of the ancient ​Constantine Bridge, giving Bulgarian archaeologists a rare opportunity ‌to document what they describe as one of the Roman Empire’s most impressive engineering achievements.

A succession of record-breaking heatwaves in Europe this ​summer has caused a severe drought in parts ​of the continent, affecting major waterways such as ⁠the Danube and the Rhine.

“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.”

The bridge, commissioned by Emperor Constantine I and ‌inaugurated ⁠in A.D. 328, linked the ancient city of Ulpia Oescus with Sucidava in what is now Romania. Stretching more than 2 km (1.2 miles), it is regarded as one ​of the ​longest bridges of ⁠antiquity, though short-lived. It is believed to have been largely destroyed around A.D. 367.