Editors. "Imperial force besieges the fortress of Jülich". The Literary Encyclopedia. First published 01 February 2011
[http://www.litencyc.com/php/stopics.php?rec=true&UID=15668, accessed 24 May 2013.]
Archduke Leopold of Austria lays siege to the fortress of Jülich on behalf of Holy Roman Emperor Rudolf II, who is attempting to claim the Duchy for his own.