Letters from <a href="https://en.wikipedia.org/wiki/Sigrid_Undset" class="extiw" title="w:Sigrid Undset">Sigrid Undset</a> to <a href="https://en.wikipedia.org/wiki/Nini_Roll_Anker" class="extiw" title="w:Nini Roll Anker">Nini Roll Anker</a> during the first World War.
<bdi><a href="https://en.wikipedia.org/wiki/en:Sigrid_Undset" class="extiw" title="w:en:Sigrid Undset"><span title="Norwegian writer (1882-1949)">Sigrid Undset</span></a>
</bdi>
1918-01-01
The National Archive of Norway, via <a rel="nofollow" class="external text" href="http://www.europeana1914-1918.eu/en/contributions/21410">Europeana 1914–1918</a>