The first settlement in the area of today’s Celje emerged in the Hallstatt period. Among the Celts and to ancient Greek historians, it was known under the name of Keleia, which in the old Celtic language meant ‘shelter.’ In the 1st century BC, it grew into a well-established Celtic town, where the currency of the Kingdom of Noricum was coined.
In the year 15 BC, the town was conquered by the Romans and its name Latinised into Celeia. In 45 AD, under the rule of the Roman Emperor Claudius, it was granted civic rights as municipium Claudia Celeia.

Ravaged during the Migration Period in the 5th and 6th centuries, the town was rebuilt in the early Middle Ages. The earliest medieval record of it was in Annales Admontenses (written between 1122 and 1137), where it was referred to as Cylie and stated to be the seat of a margrave.

Celje received civic rights on April 11, 1451, by the order of Frederick II, Count of Cilli. When the Counts of Cilli died out, the town was taken over by the House of Habsburg and rapidly developed into a craft and commercial centre.

In 1867, following Austria’s defeat in the Austrian-Prussian war, Celje became part of the Austro-Hungarian Empire.