Rosenburg Castle, Medieval castle ruin in Herisau, Switzerland

Rosenburg Castle is a ruined hilltop castle on the Ramsenstock at 926 m, west of Herisau, also called Ramsenburg. It consists of a residential tower (Bergfried) with a high entrance, residential buildings and a surrounding wall, enclosed by a deep ditch. The tower measures 9.2 by 9.7 m with walls 2.2 to 2.9 m thick.

The fortress was established around 1150 by the Rorschach family as a territorial stronghold in the region. A major attack and fire in 1403, triggered by local resistance to the authority of the Abbot of St. Gall, led to its destruction and abandonment.

The castle's name comes from the rose bush in the coat of arms of the Rorschach family, who built it around 1200; a second castle, Rosenberg, stood about 2.3 km away. In the 14th-century chronicle of Johannes von Winterthur, the two Rosenburg brothers, both named Rudolf, no longer lived here and a farmer held the castle for them.

The ruin stands on the wooded Ramsenstock at 926 m, about one kilometre south of Ramsen and west of Herisau. The tower entrance lies roughly 4.4 m above the ground, so the interior is not entered from the base. The walls and ditch are best seen on foot along the hill paths; the ground is uneven.

The castle was smaller than nearby Rosenberg, about 2.3 km away. A 14th-century chronicle by Johannes von Winterthur tells that two knights and their servants came to evict the farmer holding Rosenburg for the two Rudolfs; the farmer killed both knights inside and their servants in the stables. The tower entrance lies about 4.4 m above ground.