<p>Adoption of the Polish Constitution of May 3, 1791.
</p><p>The painting depicts King Stanislaus Augustus together with members of the Grand Sejm and inhabitants of Warsaw entering St John's Cathedral in order to swear in the new national constitution just after it had been adopted by the Grand Sejm in the Royal Castle visible in the background.
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May 3rd Constitution was the first written national constitution in Europe, and the world's second, after the United States Constitution. The May 3rd Constitution was adopted by the Sejm of the Polish-Lithuanian Commonwealth on May 3, 1791
<bdi><a href="https://en.wikipedia.org/wiki/en:Jan_Matejko" class="extiw" title="w:en:Jan Matejko"><span title="Polish painter (1838-1893)">Jan Matejko</span></a>
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National Museum of Poland Catalogue (for better resolution: calendar with pictures of Matejko)