The Palatinate near Kaub, sometimes incorrectly called the Rhine Palatinate or Pfalzburg, is actually called Pfalzgrafenstein. The island castle on the Weisenau cliff could serve much better as a customs tower in the middle of the river, since Gutenfels Castle was far too far from the shore. Emperor Ludwig the Bavarian (1314-1347) left a customs tower in a surprising action between August 1326 and July 1327 erect. Pope John XXII. wrote to Count Robert von Virneburg in 1327 that he was writing letters to the archbishops of Cologne about the Rhine toll set up by Ludwig the Bavarian near the castrum Caub and the strong tower (turrem fortissimam, castrum turrem) built by Ludwig there on a Rhine island to enforce the toll , Mainz and Trier. He admonishes the count to support the princes of the church in the planned elimination of the toll and the destruction of the toll tower. In 1326/1327 only the central pentagonal tower was built. It was built pentagonally, since the upstream tip was to serve as a flood and ice breaker. Between about 1338 and the end of 1342, lumber was dispatched for the construction of the castrum Pfalzgrafenstein am Zoll in Ehrenfels. The wood was needed for the 12 m high hexagonal wall that was built around the tower at the time. The king gave the castle to his Wittelsbach relatives in Heidelberg. In 1339 the two Counts Palatine Ruprecht d.Ä. and Ruprecht the Younger a perpetual truce for their town of Kaub and for Pfallentzgrafenstein Castle, which is so named here for the first time. The castle, which was extended again in 1607, remained undamaged in the hands of the Palatinate until 1803. on the southern tip of the bastion there is still a lion enthroned as holder of the Palatinate coat of arms (copy). After the dissolution of the electoral state, the complex fell first to the Duchy of Nassau, then in 1866 to the Prussian state. It remained a customs station until 1876. It has been owned by the state of Rhineland-Palatinate since 1946 and was used as a signaling station for Rhine shipping. It was completely renovated in the 1960s and 1970s.
Source:
regionalgeschichte.net/mittelrhein/kaub/kulturdenkmaeler/pfalzgrafenstein.html