Nis is one of the oldest cities in the Balkans and one of the largest cities in Serbia, with over 250,000 people. It is located along the Nišava River and surrounded by mountains. Nis is known as the birthplace of the Roman emperor Constantine the Great and is an important cultural and historical center, containing many monuments and cultural institutions like the National Theatre. The city also hosts numerous annual festivals and is a center for sports in Serbia.