- http://scihi.org ferdinand-freiherr-von-richthofen-silk-…
- geni.com people/Ferdinand-Friedrich-Georg-Ludwig-…
- wikiwand.com en/Christoph_Friedrich_Nicolai
- hmn.wiki tr/Friedrich_Nicolai
- ww2gravestone.com people/schleicher-kurt-von/
- kolybanov.livejournal.com 19077190.html
- second.wiki wiki/karl_ferdinand_friedrich_von_…
- gettyimages.com detail/illustration/friedrich-…