Editors. "League of Heidelberg is formed by German princes". The Literary Encyclopedia. First published 01 November 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=14847, accessed 19 May 2013.]
Both Catholic and Protestant princes in Germany join together to form a League of Heidelberg, aiming to preserve peace, as well as to prevent the election of Philip of Spain as the next Holy Roman Emperor.