Søborg Castle, in its heyday, was the strongest castle in Denmark, and was also used as a prison. It was inhabited until the Count's Feud in 1535, when it is speculated that it was destroyed. In 1577, the feudal tenant was granted permission to use the ruins as a quarry.
Søborg Castle is first known from the 12th century, when ownership of the castle passed from the king to the bishop of Roskilde. Traditionally archbishop Eskil of Lund is said to have expanded the previous buildings to a real castle with defensive walls and a moat. As Eskil was in close contact with Esrum Abbey, it is considered likely that he lived nearby at Søborgby.
In 1985, Robert Egevang and Søren Frandsen took the initiative of digging two trenches to make clear the conditions between the octagon tower and the castle proper. A rampart approximately 11 meters wide is the oldest encirclement of the castle. In the rampart, as well as in the octagon tower which was built at the same time, tiles have been found. The excavations show that the castle proper was erected in the late 13th century, which would make it unlikely that Eskil was the builder, as he died in 1181. The tiles are very unevenly made, evidence of their novelty in Denmark, after having only recently arrived from Lombardy.
In the Middle Ages, the castle was on an island in a fjord with an outlet to the Kattegat by Gilleleje. Later, the fjord became Søborg Sø, which was drained 1872-1896 when a canal was dug to Gilleleje.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.