Rujan ( sr-Cyrl, Рујан) or Rujen (), is a mountain in southern Serbia, near the town of
Bujanovac
Bujanovac ( sr-cyr, Бујановац, ; sq, Bujanoc) is a town and municipality located in the Pčinja District of southern Serbia. Situated in the South Morava basin, it is located in the geographical area known as Preševo Valley. It is also ...
. Its highest peak ''Kalje'' has an elevation of above sea level. On the mountain, there is Kale-Krševica archeological site, dating from the 13th century BC. The Pčinja flows through the valley of Rujen.