Celje Castle (also known as Celje Upper Castle or Old Castle) (Slovene Celjski grad, Celjski zgornji grad or Stari grad) is a castle ruin in Celje, Slovenia, formerly the seat of the Counts of Celje. It stands on three hills to the southeast of Celje, where the river Savinja meanders into the Laško valley. Today, the castle is in the process of being restored. It was once the largest fortification on Slovenian territory.
The earliest reference to Celje Castle dates from 1322 and calls it “purch Cylie”. Later, the castle was known by various names, including “vest Cili” (1341), “castrum Cilie” (1451), “gsloss Obercili” (1468). It is noteworthy that the name “Obercili” - Upper Celje - only appears after the Counts of Celje had died out. Its original name was “grad Celje” (Celje Castle).
The first fortified building on the site (a Romanesque palace) was built in the first half of the 13th century by the Counts of Heunburg from Carinthia on the stony outcrop on the western side of the ridge where the castle stands. It had five sides, or four plus the southern side, which was a natural defence. The first written records of the castle date back to between 1125 and 1137; it was probably built by Count Gunter. In the western section of the castle, there was a building with several floors. Remains of the walls of this palatium have survived. In the eastern section, there was an enclosed courtyard with large water reservoirs. The eastern wall, which protects the castle from its most exposed side, was around three metres thicker than the rest of the curtain wall. The wall was topped with a parapet and protected walkway. This was typical of Ministerialis castles of the time.
The first castle was probably burned and destroyed in the fighting between the Lords of Sanneck and the Lords of Auffenstein. The gateway was later moved from the northern side by freemen loyal to the Lords of Sanneck. They gave the castle a new curtain wall and reinforced this with a tower on the northern side, which guarded the entrance to the inner ward, sometime before 1300. The new wall reached from a natural cliff in the east to the remains of the earlier wall in the northeast. The entrance was moved to the southern side, where it still is today.