On the banks of the Moselle, a Rhine tributary, Trier is near the Luxembourg frontier, about 100km (60 miles) southwest of Koblenz. It is the oldest city in Germany, a Roman imperial capital in the thirrd and fourth centuries AD, and a UNESCO World Heritage Site. Attractions include The Porta Nigra (city gate, second century); Roman Imperial Baths; Basilica; Amphitheater; Cathedral (fourth century); Gothic Church of Our Lady; Simeonsstift with 11th-century cloisters; Church of St Matthew (Apostle’s grave); Church of St Paulinus (designed by Balthasar Neumann); Regional Museum; Episcopal Museum; Municipal Museum; Municipal Library (with notable manuscripts); and the birthplace of Karl Marx.