Treysa, an independent town until 1970, is the biggest Stadtteil of the German town Schwalmstadt. It was incorporated into Schwalmstadt in December 1970. The location around Treysa and Schwalmstadt is called Schwalm. The historic city lies on a hill which is up to 35 meters higher than the valley where the river Wiera enters in the Schwalm. To protect the city of floods, a detention basin had been built. During the 8th century, the city Treise was a part of the Hersfeld Abbey.