Hohe Domkirche St. Peter zu Trier was completed in 1270, making it Germany’s oldest Roman Catholic cathedral. The stone Romanesque façade of the Cathedral of Trier gives this UNESCO World Heritage Site the appearance of a medieval castle. Inside are the relics of Saint Helena. She was an empress, the mother of Constantine the Great, and the first Christian emperor of Rome. Helena claims to have discovered the True Cross of Christ’s crucifixion in 328 AD.