Celje (tsĕˈlyĕ) [key], city (1991 pop. 40,710), in Slovenia. Metallurgy, chemicals, and food processing are the chief industries. Founded (1st cent. A.D.) by the Roman Emperor Claudius, it was the seat (1341–1456) of the powerful Slovenian counts of Celje (or Cilli). In the city are a 13th-century monastery and a 16th-century palace.