Editors. "Peace negotiations are renewed in Cologne and Hamburg". The Literary Encyclopedia. First published 01 February 2011
[http://www.litencyc.com/php/stopics.php?rec=true&UID=16134, accessed 21 April 2014.]
Peace negotiations aiming to end (what was later to become known as) the Thirty Years War are renewed in Cologne and Hamburg. At this point it had already been going on for two decades.