It was never forgotten in time or abandoned. It was still used for the coronation of the imp. aug. for a long time and was visited by most of them regularly. Most medieval imp. aug. didn't not have something that could be called preferred city or capitol, and Barbarossa was one of them. So Aachen is a bit of a stretch (but better than 'Barbarossa's court', right?), but it is still the most plausible for him. It's true that Charlemagne spend a lot of his time in his later life in the Kaiserpfalz in Aachen that he built. But he also built Kaiserpfalzen in Ingelheim and newly conquered Paderborn that were of quite some importance. If you look at Aachen even today, the Kaiserpfalz is still visible in the city layout. It is, for a variety of reasons, nearly completely built over though. Charlemagne's throne (and the incredible building surrounding it) are still there.Aachen for Barbarossa? That's quite interesting. I thought Aachen was only capital for Charlemagne, and then abandoned/forgotten in time.