The <a href="https://en.wikipedia.org/wiki/Treaty_of_Frankfurt_(1539)" id="mwPA" rel="mw:WikiLink" title="Treaty of Frankfurt (1539)">Treaty of Frankfurt</a> between Protestants and the Holy Roman Emperor is signed.<sup about="#mwt31" class="mw-ref reference" data-mw='{"name":"ref","attrs":{},"body":{"id":"mw-reference-text-cite_note-4"}}' id="cite_ref-4" rel="dc:references" typeof="mw:Extension/ref"><a href="./April_19#cite_note-4" id="mwPQ" style="counter-reset: mw-Ref 4;"><span class="mw-reflink-text" id="mwPg">[4]</span></a></sup>
<span class="mw-reference-text" id="mw-reference-text-cite_note-4">Smith, <i id="mwBXA">The Age of the Reformation</i>, p. 122.</span>