Before the castle was built, the Calenberg rose some 10 metres (33 ft) above the water meadows between the river arms of the Leine that existed at that time.

The name Calenberg clearly indicates that the chalk marl stratum was not tree-covered, but stood proud of the Leine meadows as a "bare hill".

The old water castle was built on the island of Calenberg as a lowland fort in the middle of the River Leine, which used to form the border of the Prince-Bishopric of Hildesheim.

Although the castle had an important location as a border fortification, it was enfeoffed as early as 1327 to the knight, Conrad of Saldern, due to a lack of funding.

The von Saldern family had to relinquish the castle in 1364 to Duke William because they had participated in a secret pact with the Bishop of Hildesheim.

In 1371 the castle became the seat of the ducal advocates (Vögte) in the 'Grand Advocacy' (Großvogtei) of Calenberg and, in 1432, it was named as a Residenz for one of the Welf dukes.

At the beginning of the 16th century, and before the Hildesheim Diocesan Feud, it was therefore rebuilt under Eric I into a modern fortress, accessible over two bridges.

In front of the western entrance with its drawbridge, an unfortified 'island' (Vorwerksinsel) was laid out and given the field name Die Bleiche.

In the Thirty Years' War the fortress of Calenberg was besieged in 1625 for three weeks by Tilly and it was surrendered only after a mutiny by the troops.

In 1632 the Welf duke, George of Brunswick-Calenberg, fighting on the Swedish side, did not initially succeed in retaking the castle despite a six-week siege.

The fortress helped to reduce the influence of the bishops of Hildesheim, with whom the Welfs lived in constant conflict, in the region of Hanover and to achieve territorial gains.

In 1636, Duke George of Brunswick-Calenberg recaptured the territory for the House of Welf during the Thirty Years with the help of Swedish troops, and chose Hanover as a residence.

As a result, on 2 November 1549, Eric II placed Anton Corvinus and Walter Hoiker in custody in Calenberg Fortress for contempt to force them and the other clergy to accept the Interim.

After the Peace of Passau, when the Emperor declared the Interim invalid and Eric II had fallen out of favour with him, the two prisoners were released on 21 October 1552.

In 1654 Caspar Merian (1627–1686) published his copperplate of Calenberg Fortress in Topographia Germaniae Braunschweig-Lüneburg,[3] which was based on a sketch by survey engineer, Conrad Buno.

In the background are the fortifications of Calenberg enclosing various buildings (A. Das Schloss) with a house for employees on the defensive island in front of the fortress.

To the right of the fort are the houses of Lauenstadt (D. Lawenstat); in front of them, on the near bank of the Leine (G. Leina Fluss), is the Calenberg Mill (C. Die Mühle).

The gallows were later replaced by a new execution site, Das neue Gericht, which was located northeast of the present intersection of the B 3 road with the L 460.

South of it stood the accommodation for the prison warders and the legal staff (Gerichtsboten); here there were two detention cells with barred windows.

A row of two half-timbered houses dating from 1830 stood centrally on the foundation of the west wing of the early 14th-century castle.

In the 19th century King George V of Hanover built Marienburg Castle on nearby Schulenberg Hill for his wife Marie of Saxe-Altenburg.

After the annexation of the Kingdom of Hanover by Prussia in 1866, Marienburg remained in private ownership while Calenberg Castle and its royal demesne became state owned.

As of 2007[update], in good weather an ecumenical church service has been held in the morning of Ascension Day in the southern part of Calenberg Castle since the end of the 20th century.

A bridge over the River Leine between Calenberg Fortress and the village of Schulenburg is mentioned in records dating back to 1363.

Tragically, Conrad Kösel and Rudolf Ohlmer were shot dead in their car during the retreat on the K 506 road just before Adensen by the advancing tanks of the US Army.