Archaeologists have spotted the remains of a mile-long ancient structure built by the Romans in the shallow summer waters of Europe’s second-longest river.
The foundations of Constantine’s Bridge, first assembled almost 1700 years ago, have slowly surfaced from the waters of the Danube, as a major summer drought affecting Europe has caused the river’s waters to recede.
Within the unusually shallow waters, the ancient Roman bridge recently made a rare appearance near the village of Gigen, Bulgaria.
An Ancient Roman Marvel Resurfaces
Built in A.D. 328, the mile-long bridge was constructed under the reign of Constantine I. At the time of its use, it was the single longest Roman-built bridge anywhere in the ancient world.
It is believed that the bridge’s construction was based on Trajan’s bridge, an earlier engineering marvel conceived by Apollodorus of Damascus. Coinciding with the first use of Constantine’s bridge was a unique gold medallion, of which only two copies have survived. Minted in Rome, the medallions memorialized the structure’s completion and inauguration.
Connecting modern-day Romania with parts of Bulgaria, archaeologists believe the ancient structure was likely destroyed within decades of its assembly, having likely fallen by around A.D. 367.
At the height of its use, it once stretched from close to the modern Bulgarian city of Pleven, Bulgaria, to present-day Sucidava in Romania.
Еха!
На 4.08. екип на Регионален исторически музей – Плевен документира културните останки (базите) на Константиновия мост при античната столица Улпия Ескус (с. Гиген).
Мостът е най-дългото мостово съоръжение през р. Дунав, открит на 5 юли 328 г. от император Константин I. pic.twitter.com/SulQykXWp2— Venelin Molnar (@VenelinMolnar) August 6, 2026
Drones Reveal a Sunken Ancient Structure
With the help of drones, the ancient structure’s foundations were successfully mapped by Pavel Popov of the Pleven Regional Historical Museum, which helped to capture data that showcases the ancient structure’s magnitude.
The unprecedented summer heat affecting Europe this year has affected many famous waterways, which include the Rhine, according to The Greek Reporter.
Having remained below the Danube’s waters for many centuries, the bridge’s reappearance marks an unusual opportunity for researchers to glimpse this ancient engineering marvel of the Roman world.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.