Dorsten is situated on the western rim of Westphalia bordering the Rhineland. Its historical old town lies on the south bank of the river Lippe and the WeselβDatteln Canal and was granted city rights in During the twentieth century, the town was enlarged in its north by the villages of the former Herrlichkeit Lembeck.
The exact linguistic derivation of the word "Dorsten" is unknown, leaving the meaning of the town's name unclear. Archaeological findings show that the area was already populated during the Neolithic and Bronze Ages, from about BC onwards. From around AD onwards, the Archbishopric of Cologne began to evangelise the area around Dorsten. Archbishop Konrad von Hochstaden , together with the Count of Cleves , granted Dorsten the city rights in Due to its economically favourable position on the river Lippe, the town became a member of the Hanseatic League of international trading cities and turned into the richest town in the Vest Recklinghausen.
In , Franciscan friars established a friary which continues to exist today as the world's oldest permanently existing cloister of this order. The monks founded Gymnasium Petrinum in and in the Ursulines set up a cloister including a boarding school for girls.
However, the Thirty Years' War β48 , the Hessian War and the continuous occupation by various forces badly derogated Dorsten's medieval wealth. On 9 February , Hesse-Cassel captured the town of Dorsten without resistance from the Electorate of Cologne and the Vest of Recklinghausen and, in the years that followed, it was turned into the strongest fortress in the region. As a result, attempts were made to recapture it.
The first siege in was unsuccessful, but in , a second Siege of Dorsten resulted in considerable destruction of the town and the eventual surrender of the garrison.
