I went to Germany last week to find the Holy Grail but on the way I stopped off at Aachen to take a look at the chapel that Charlemagne built for himself shortly after the year 800.

It was, they say, the tallest domed building north of the Alps at the time, though I can’t think of many others. It’s like an octagonal tea caddy lined with marble and mosaics, in the manner of San Vitale in Ravenna. In fact Charlemagne took from Ravenna some ancient monolithic columns for it, and a thousand years later the French plundered half of them and took them off to Paris, where they remain.