Heisterbach Abbey was a Cistercian monastery in the Siebengebirge near Oberdollendorf. The tradition of its origin is that a knight named Walther lived as a hermit on the Stromberg, also known as the Petersberg, one of the mountains forming the Siebengebirge. When numerous disciples began to settle near his cell, he built a monastery in 1134, where the community lived according to the Rule of St. Augustine. After the death of Walther however his disciples left the monastery on the Petersberg and built another on the Sulz.
In 1189 Philip, Archbishop of Cologne, requested Gisilbert, abbot of the Cistercian Himmerod Abbey in the Bishopric of Trier, to re-settle the deserted monastery of Petersberg with Cistercians from Himmerod. On 22 March 1189, therefore, twelve Cistercian monks with the newly appointed Abbot Hermann took possession of it.
Three or four years later they moved to the foot of the mountain, where they built a new monastery which they called Petersthal or Heisterbach, which was the name which prevailed.
The famous basilica of Heisterbach was begun by Abbot Gerard (1195–1208), and consecrated in 1237 under Abbot Henry (1208–1244). Being built during the period of transition from the Romanesque round arch to the Gothic pointed arch, its style of architecture was a combination of the Romanesque and the Gothic.
Heisterbach, which had large possessions and drew revenues from many neighbouring towns, remained one of the most flourishing Cistercian monasteries until its suppression in 1803. The library and the archives were given to the city of Düsseldorf; the monastery and the church were sold and torn down in 1809, and only the apse with the ruins of the choir remains.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.