The Ahlsburg or Alerdestein was an imperial castle

Castle

A castle is a type of fortified structure built in Europe and the Middle East during the Middle Ages by European nobility. Scholars debate the scope of the word castle, but usually consider it to be the private fortified residence of a lord or noble...

 near Stapelburg

Stapelburg

Stapelburg is a village and a former municipality in the district of Harz, in Saxony-Anhalt, Germany. Since 1 January 2010, it is part of the municipality Nordharz....

 in the present-day district of Harz, in the German state of Saxony-Anhalt

Saxony-Anhalt

Saxony-Anhalt is a landlocked state of Germany. Its capital is Magdeburg and it is surrounded by the German states of Lower Saxony, Brandenburg, Saxony, and Thuringia.Saxony-Anhalt covers an area of...

.

Location

The site of the former Ahlsburg is located about 4.5 km south-southwest of Stapelburg and 4 km north-northeast of the Ecker Reservoir on the northern edge of the Harz mountains. It is on the eastern bank of the Ecker

Ecker

Ecker is a river in Germany. It may also refer to:Entertainment*Meng and Ecker As a name:*Danny Ecker*Janet Ecker*Guy Ecker*Haylie Ecker*William Ecker*Tyler Ecker*Enrique Ecker*Alexander Ecker*Johnny Ecker...

, a south-eastern tributary of the Oker

Oker

The Oker is a river in Lower Saxony, Germany, that has historically formed an important political boundary. It is a left tributary of the River Aller, in length and runs in a generally northerly direction.- Course :...

 that forms the state border with Lower Saxony

Lower Saxony

Lower Saxony is a German state situated in north-western Germany and is second in area and fourth in population among the sixteen states of Germany...

 to the west. The castle was situated above a narrow section of the valley, where a footbridge crossed the Ecker, on a spur

Spur

A spur is a metal tool designed to be worn in pairs on the heels of riding boots for the purpose of directing a horse to move forward or laterally while riding. It is usually used to refine the riding aids and to back up the natural aids . The spur is used in every equestrian discipline...

 with steep granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

 crags.

History

The castle was first mentioned in documents as Alerdestein in 1357, when Emperor Charles IV  enfeoffed Alard the Elder and Alard the Younger of Burgdorf with 1 ½ hides in Wollingerode that "belong to the Alerdestein". It was part of the imperial estate and the palace of Werla. In the early modern period, the castle fell into ruin. Ownership passed to the Count of Stolberg.

The lords of the castle were responsible for protecting the surrounding imperial forest.

Later the Inner German Border passed through the birch

Birch

Birch is a tree or shrub of the genus Betula , in the family Betulaceae, closely related to the beech/oak family, Fagaceae. The Betula genus contains 30–60 known taxa...

pioneer forest. On a right-hand bend in the former Kolonnenweg, there is a signpost to, amongst other places, "Ahlsburg", which runs uphill from the Ecker for about 100 metres.

Today, only a few vestiges of the Ahlsburg remain.