I noted the title of this article with interest. The blogger who relayed the story from a newspaper in Bingen answers the question thus: "As it's Germany, the Roman wall wins."

Important Boppard finds from Roman times feature in a new archaeological park in the town. Dominating the site and the top of Kirchgasse is a massive fortress curtain wall, some 60 metres long and eight metres high. The wall linked two towers of a huge Roman fort that once stood at the side of the Rhine.

Astonishing experts by its excellent preservation, the wall came to light when workmen began digging for a multi-storey car park - a project soon abandoned. Apart from similar remains in the UK, the finds were judged to include the best section of a Roman wall of this period uncovered anywhere north of the Alps.

Other items found included 12 graves made from stone tiles. Cloth fragments indicated that the graves were of Christians buried in the 7th or 8th centuries. Also uncovered was the cellar of a fortress-house, with wall apertures for archers, from the 12th and 13th centuries, and the remains of a horse-mill.

The wall was used at least through the 13th century. I wonder when it got covered up?

That casual opening remark about Germany, though; that suprised me--and then it made me think of something that Belloc said in The Path to Rome:

The German spirit is a marvel. There lay Porrentruy. An odd door with Gothic turrets marked the entry to the town. To the right of this gateway a tower, more enormous than anything I remembered to have seen, even in dreams, flanked the approach to the city. How vast it was, how protected, how high, how eaved, how enduring! I was told later that some part of that great bastion was Roman, and I can believe it. The Germans hate to destroy. It overwhelmed me as visions overwhelm, and I felt in its presence as boys feel when they first see the mountains. Had I not been a Christian, I would have worshipped and propitiated this obsession, this everlasting thing.