Trajan's Bridge was a Roman segmental arch bridge located at the border of modern-day Serbia and Romania. It was the first bridge to cross the lower Danube and was, for 1000 years, the longest arched bridge in the world.
The bridge was constructed in 105 AD under the command of Emperor Trajan.
Only some of the bridge's piers remain today. None of the piers that spanned across the water remains, but on each side of the border, you can see the remaining piers.