Tourists are drawn to the German city of Trier for a taste of ancient Rome. Trier is 120 miles (193km) southwest of Frankfurt and was founded as a colonial capital under Roman Emperor Augustus in 16 BC, making it Germany's oldest city. The city became an important political and cultural centre, and many Roman buildings and monuments remain to be explored by visitors. In fact, the city has at least five UNESCO World Heritage Sites: St Peter's Cathedral, a remarkable 11th-century church holding several significant tombs; The Black Gate (Porta Nigra), the only remaining ancient gate into the city, which dates back to about 180 AD; The Imperial Roman Baths, 2,000-year-old ruins of a bath complex once frequented by Constantine; the Church of Our Lady, another beautiful old church adjacent to the cathedral; and the Amphitheatre, an enormous ruin dating back to the 2nd century. The Hauptmarkt, or central square, has great markets and is especially jolly over the Christmas season when it hosts one of Germany's famous Christmas markets. Trier is also a good starting point for trips into the Mosel Valley, Germany's main wine-producing region and a good area to explore if you want to visit vineyards and wine cellars. Another popular excursion from the city is a cruise on the scenic Mosel River.