Clèves is now called Kleve. It is located in the State of Nordrhein-Westfallen in Germany. It is near Nijmegen, The Netherlands, and the Rhein. The whole area was vigorously contested in 1944-1945 and Kleve was bombed by the allies as an obstacle to crossing the river.
According to the Wikipedia historical article, back in the heyday Kleve was a duchy. "The duchy's territory roughly covered the present-day German districts of Cleves (northern part), Wesel and the city of Duisburg, as well as adjacent parts of the Limburg, North Brabant and Gelderland provinces in the Netherlands."