Trier is the oldest city in Germany and there was a time when it was the second most important city in the Roman Empire after Rome itself - and it shows. I have rarely seen a city with such an impressive array of monuments from Antiquity onwards through many time periods up to the present day - a veritable cross section of European history that is remarkably well preserved (sometimes it helps to be off the beaten track). Of course, Roman and medieval monuments dominate the scene, especially the world-famous Porta Nigra (don't neglect to go inside), the cathedral and the Church of Our Lady next door. The city's history is especially connected to Emperor Constantine the Great and the conversion of the Empire to Christianity. I visited Trier for the huge exposition on Constantine on the 1700th anniversary of his marriage in Trier, which was great, but the city itself impressed me even more.