Niš, a city in Serbia's Nišava District, is one of the oldest cities in the Balkans and Europe, and has from ancient times been considered a gateway between the East and the West. The Paleo-Balkan Thracians inhabited the area in the Iron Age, and Triballians dwelled here prior to the Celtic invasion in 279 BC which established the Scordisci as masters of the region. Naissus was among the cities taken in the Roman conquest in 75 BC. The Romans built the Via Militaris in the 1st century, with Naissus being one of the key towns. Niš is also notable as the birthplace of Constantine the Great, the first Christian Roman Emperor and the founder of Constantinople, as well as Constantius III. It is home to one of Serbia's oldest Christian churches dating to the 4th century in the suburb of Mediana.