Eric of Pomerania
The Sound Dues (or Sound Tolls; ) were a toll on the use of the Øresund, or "Sound" strait separating the modern day borders of Denmark and Sweden. The tolls constituted up to two thirds of Denmark's state income in the 16th and 17th centuries. The dues were introduced by King Eric of Pomerania in 1429 and remained in effect until the Copenhagen Convention of 1857 (with the sole exception of Swedish ships between 1660 and 1712). Tolls in the Great Belt had been collected by the Danish Crown at least a century prior to the establishment of the dues by Eric of Pomerania.