This river, together with the nearby Leda forms the so-called East Frisian Mesopotamia, the Leda-Jümme area.

Both rivers were important trade routes in the Middle Ages and early modern times, because they flowed in an east-west direction.

This fortress had been part of a border defense line against the adjacent County of Oldenburg and secured access to East Frisia.

[2] After the Schlüsselburg fortress had been destroyed and rebuilt several times, it lost its importance after the construction of Stickhausen Castle and is no longer mentioned in documents.

After the Reformation, Countess Anna built an outer wall in 1558 using stones from the abandoned Barthe Abbey and from Uplengen Castle, which had been razed in 1535 at the behest of Count Enno II.

They completed the expansion of the fortress by building a fortified substation as a complement to the existing ravelin and the actual castle.

The entire complex comprised at that time a three-winged main castle with corner tower, the old bailey to the gatehouse, stables, peat barn, burgrave's mansion and garrison church on the upper floor of the gatehouse, outer wall with powder tower and a ravelin on the south side, between the Jümme and the main complex.

After Prussia gained control of East Frisia in 1744, the castle no longer served any purpose and Frederick the Great ordered it razed.