Until now, the date of construction of Trier's Porta Nigra, the largest Roman city gate north of the Alps, could only be estimated.
Researchers dated it back to somewhere between 150 AD and 320 AD.
Scientists have now managed to determine exactly when the city gate was built, thanks to ancient wood that was found in archaeological digs.
Watch video 01:01 World Heritage Site: Trier
The largest Roman monument of its kind in Germany, it is part of a UNESCO World Heritage Site ensemble, called the Roman Monuments, Cathedral of St. Peter and Church of Our Lady in Trier.