The castle of Alt Dahlen, belonging to the Riga bishopric, along with the nearby Holme stronghold was the protection point of the city of Riga from the land side and it additionally controlled the navigation on the nearby river. Initially, these areas were given to the knight Johannes de Dolen, however, it was soon realized the strategic importance of this place and already in 1226 Dahlen passed under the management of the Riga cathedral chapter. During the first major dispute between the Teutonic Knights and Riga, in the second half of the 13th century, the order troops completely destroyed the castle of Alt Dahlen, as well as the nearby Holme. The castle has never been rebuilt, although the archbishopric has made efforts to regain the lost possessions. They ended with success in 1318, when, on the order of Pope John XXII, the Order turned the chapter some of the stolen goods. Although Alt Dahlen remained in ruin, on the opposite, southern side of the island, a new castle Neu Dahlen was erected, mentioned in sources for the first time in 1359.
Alt Dahlen castle was a simple defensive site erected originally on the island, around a rectangular walled courtyard, to which a single gate located in the middle of the eastern wall, was led. The stone foundations of a small, wooden building were discovered next to it. Brick buildings were limited to two houses, located in the western corners of the courtyard, from which the north-west building from the side of the river Daugava had a somewhat thicker foundations, which suggests that it could have been a tower.
The only remains of the castle Alt Dahlen are partially exposed, about a meter high ruins.
Borowski T, Miasta, zamki i klasztory, Inflanty, Warszawa 2010.