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In 1801, Louis Engelbert, Duke of Arenberg, Prosper's father, lost the former Duchy of Arenberg on the left bank of the Rhine but received a larger duchy on the right bank in 1803.
color:red from:1804 till:1809 shift:(-26,15) text:Arenberg
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During the secularization of the ecclesiastical states in 1802–03, also known as the German Mediatisation, the electorate was abolished and Vest Recklinghausen was annexed by the Lords of Arenberg.