Flag of the King of Poland and Supreme Duke of Lithuania <a href="https://en.wikipedia.org/wiki/Jogaila" class="extiw" title="w:Jogaila">Jogaila</a> with the Polish Eagle and Lithuanian <i><a href="https://en.wikipedia.org/wiki/Coat_of_arms_of_Lithuania" class="extiw" title="w:Coat of arms of Lithuania">Vytis (Waykimas)</a></i>, used during the <a href="https://en.wikipedia.org/wiki/Council_of_Constance" class="extiw" title="w:Council of Constance">Council of Constance</a> from 1414 to 1418. Painted in 1416.
From an Armorial (a book of coats-of-arms), produced in 1416. Made by a Portuguese herald, attending the Council of Constance.
1416
<a rel="nofollow" class="external free" href="https://iiif.biblissima.fr/collections/manifest/04f2cc0d807d3d80e1408351acf5f1500fcc4888?tify=%7B%22pages%22">https://iiif.biblissima.fr/collections/manifest/04f2cc0d807d3d80e1408351acf5f1500fcc4888?tify={%22pages%22</a>:[115],%22panX%22:0.399,%22panY%22:0.726,%22view%22:%22export%22,%22zoom%22:0.487} (page 85 in the actual book; page 115 in the online version)