Together with the palace an outer bailey was placed on the island containing the houses of the Burgmannen, a settlement in its own right independent from the town of Gelnhausen until the beginning of the 19th century.

The Gelnhausen palace also controlled the important long-distance highway Via Regia between Frankfurt and Leipzig as it passes through the valley of the Kinzig river.

Debate revolved around the question of whether the building of the palace took place a few years before the official founding of the royal town in 1170.

[2] In 1992 it was possible to extract several poles of the wooden sub construction from under the gate building during restoration works.

During the Hohenstaufen era, the palace was an Imperial Castle (Reichsburg), had a burgrave and Burgmannen.

Its estate included Büdingen Forest [de], in which the occupants of the outer bailey still retained timber rights (for construction and firewood) until the 19th century.

The decline of the palace began as early as the 14th century when, in 1349, Emperor Charles IV (HRR) enfeoffed it, together with the town, to the Counts of Schwarzburg and never reclaimed it.

After the death of Johann Reinhard III, Count of Hanau-Lichtenberg, the last male member of the House of Hanau, in 1736, the Landgraves of Hesse-Kassel inherited the Hanau half of Gelnhausen and later bought the other half owned by the Electors of Palatinate.

Around 1810, the palace became one of the first buildings from the epoch of Romanesque architecture in Germany that attracted the interest of art-loving scholars.

Not withstanding this the castle chapel, used for Protestant services between 1764 and 1811 was demolished in 1856 due to the expected costs of an otherwise necessary restoration.

Therefore, it is smoothly designed inwardly in the places where buildings adjoined, while on the rest and outwardly humped ashlars were used.

Originally, it was twice as high and its entrance was at a height of 7 m. The upper part was demolished in 1431, and replaced by a guardroom and a polygonal turret.

Based on the building connections – the interior construction was largely made of wood – it is assumed that the lower main level had a corridor behind the façade that provided access to the rooms on that floor.

According to the window arrangement, two living rooms are supposed to have been located to the west, and a hall to the east.