It was a piece of oak wood that brought the breakthrough. It lay six meters deep, well preserved in the sodden ground between stone blocks at the roman city wall near the porta nigra in trier.
The tree rings date it precisely to the winter of 169/170 AD, giving scientists the date they have long been looking for. "Now we finally know that the construction of the porta nigra began in the spring of 170," said the director of the rheinisches landesmuseum trier, marcus reuter, on friday. And added: "this is a milestone for the history of the city of trier."
And this has caused a stir far beyond the city on the mosel. For the "black gate" is considered the best-preserved romanesque city gate north of the alps and the oldest monument of its kind in the country. It was "bitter" that basically no one knew beforehand when this world-famous porta was built, reuter said. The assumptions of the researchers have so far ranged from 150 to 320 A.D. "A scientific riddle can be solved today," said rhineland-palatinate culture minister konrad wolf (SPD). This early date is a "scientifically highly significant finding".
In order to get this clarity, last autumn was dug in a place where in ancient times ran the old arm of the moselle. "We thought, in the groundwater could have preserved bauholzer", said the museum director. 25.000 euros cost the excavation, 15.000 euros came from the gerda henkel foundation. "It wouldn’t have worked without them."Then students climbed into the round shaft secured with sheet pile walls – and the crime began.
"We didn’t find anything at first. Only very few roman shards," reuter told us. One week nothing, two weeks nothing. "Then we saw that at that time the romans had put in a sheet pile wall of wood, probably to prevent the slipping of the earth during construction."Two rough boards and a round stake were then recovered. Joy in the team, but: "there we did not know yet, whether the wood can also be dated."
At the museum, the dendrochronologist mechthild neyses-eiden, who heads the research laboratory for scientific wood dating there, and her team took over. And the thriller continued. "The balks looked great at first, but were in super bad shape," she said. Some of them were so soft that they could not be prepared. "So we froze them." Then things got better. At first they got a cross-section but only a "um-datum". And then one more.
But then they found a piece of bark in a small spot on the sheet pile and with it the complete annual rings. "That gave an exact date for the year, otherwise they had only had an estimate," the expert explained. "That is already a stroke of luck."The fact that the construction date can be deduced from the date of felling is related to the following: "at that time, the wood was processed immediately after felling."
Reuter assumes that the construction of the porta nigra took one to two years. The complete city wall, about 6.4 kilometers long, probably took a few years longer to build. "But in no case as long as berlin airport and not even ten years."The part of the wall where the wood was recovered and the porta nigra were, in his opinion, built in one section.
What is special about the date of construction is that at that time there was no "military necessity", i.E. No threat, for ancient trier to build such a wall with four city gates. "This has been purely a prestige object. That was purely to show off."
Scientific proof of the age of the city gate and wall sheds light on a chapter of the city’s history in which there is still much that is unknown. "We know that trier was founded in 17 bc, but we know relatively little about how the city developed in the first 300 years," reuter said. Now many things can be reassessed.
But the porta will continue to hold one secret: why it is so black? "No one knows that," said reuter. The crust is probably due to some kind of deposits, which also protected the stone. The building is said to have been built as early as the 11th century. Century as "black gate" one designated. "In any case it was not car exhaust fumes."