Niš is the city of southern Serbia and the third-largest city in Serbia (after Belgrade and Novi Sad). It is the administrative center of the Nišava District. According to the 2011 census, the city has population of 183,164, while urban area of Niš (with adjacent urban settlement of Niška Banja included) has 187,544 inhabitants; the administrative area has a population of 260,237.It 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. It is also the birthplace of Constantine the Great, the first Christian Emperor and the founder of Constantinople, and Constantius III and Justin I. It is home to one of the oldest churches in Serbia, dating to the 4th century, located in the suburb of Mediana. Niš is one of the most important industrial centers in Serbia, a center of electronics industry, industry of mechanical engineering, textile and tobacco industry. Constantine the Great Airport is its international airport. In 2013 the city was host to the celebration of 1700 years of Constantine's Edict of Milan.