Dalaborg, Medieval castle ruins on Lake Vänern, Mellerud Municipality, Sweden.

Dalaborg is a castle ruin situated on the shores of Lake Vänern in Mellerud. The visible remains include ancient earthen ditches, defensive ramparts, a stone terrace, and the cellar foundation of a fortified blockhouse.

The fortress was built in 1304 by Duke Erik and Valdemar Magnusson as a strategic stronghold during their conflict with King Birger. It fell during the Engelbrekt Rebellion in 1434 when Swedish peasants destroyed it in their uprising.

The name Dalaborg comes from the Swedish words for valley and castle. The site is also called Dalahus in the Erikskrönikan, which describes how the local peasants were forced to build it day and night. A model of the castle, based on archaeologist Bengt Söderberg's reconstruction and the Swiss castle Mammertshofen, is on display at Mellerud Museum.

Visitors can walk through the castle grounds using marked pathways that guide you around the site. A detailed model of how the castle originally looked is displayed at the Mellerud Museum to help you visualize the structure.

The 1388 meeting at Dalaborg, where Margareta was recognised as Sweden's "fullmäktiga fru och rätta husbonde", is known as the Dalaborgtraktaten. Swedish sources note that later accounts place the signing instead at Bohus Castle, so the treaty's location is disputed.