Seal of king Louis VIII of France
Natalis de Wailly
Natalis de Wailly, <i>Éléments de paléographie</i>, tome 2, Paris, Imprimerie royale, 1838, planche D, <a rel="nofollow" class="external text" href="https://archive.org/stream/lmentsdepalograp02wail#page/344/mode/2up">voir en ligne</a>.