In 1162 Emperor Frederick I acquired cleared land from a monastery founded by Otto II, Margrave of Meissen, some of which was exchanged after the discovery of silver in 1168. In the following years, in accordance with the wishes of the founder, Hedwig of Brandenburg, wife of Otto of Meissen, the Cistercian Order undertook the establishment of an abbey on this land, into which in 1175 the first abbot with a community of twelve monks moved from Pforta Abbey (near Naumburg). The new foundation was known as Cella or Zelle Abbey. Construction of the abbey church began at this time. An intense period of construction is evidenced between 1180 and 1230, when the conventual buildings and the Romanesque portal were built. The church was dedicated in 1198, a Brick Gothic building with three aisles and a transept. The west front shows Northern Italian influences.
In 1217 supervision of the Abbey of the Holy Cross in Meissen, a Benedictine nunnery, was entrusted to the abbot of Zelle. In 1268 the abbey founded a daughter house near Guben, Neuzelle Abbey, after which the name Cella Vetus, Altzelle or Altzella gradually came into use to distinguish the older house.
As early as 1190, when Otto of Meissen died and was entombed here, the abbey served as the burial place of the Wettins, for which purpose the St Andrew's Chapel was later built, between 1339 and 1349. Both Frederick II, Margrave of Meissen, and his son Frederick III were buried there.
Under the abbots Vinzenz von Gruner and the humanist Martin von Lochau (abbot 1501-1522) the abbey enjoyed its most flourishing period. In 1436 the abbey bought Nossen Castle (Schloss Nossen) with contents and appurtenances for 4,200 Gulden. The castle itself was in poor condition and was restructured to serve as the abbot's residence. The upper storey of the lay brothers' building was converted into a library in 1506.
In 1540 Henry IV, Duke of Saxony, ordered the secularisation of the abbey. Under Augustus, Elector of Saxony, and no later than 1557, large parts of the buildings, which were in poor condition, were demolished and the materials reused elsewhere. Only the lay brothers' building remained, later used for storing grain. Between 1676 and 1787 the Electors of Saxony disinterred the remains of their ancestors and had them re-buried in a memorial chapel, the present-day Mausoleum. In about 1800 a Romantically landscaped park was established to form a picturesque setting for the building and the surrounding ruins.
References:Celje Castle was once the largest fortification on Slovenian territory. 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.