The Mystery of the Missing Medieval Plague

Medieval Wales was no stranger to disease. Throughout its history it has been beset by many plagues, from the famous Black Death to the far more obscure Yellow Plague, which is the topic of today.

The Yellow Plague, also known as Y Fad Felen, Pestis Flava, Lallwelen, and Y Dilead Melen, came and went in 6th century Wales, ending the reign of Maelgwn Gwynedd, and ravaging the kingdom of Gwynedd.

While Welsh history is full of mysteries, what exactly the Yellow Plague was, and where it went, has remained one of the most pertinent throughout history.

Chapters:
0:00 - The Dragon Tyrant
1:17 - Y Dilead Melen
4:15 - Lallwelen
8:08 - Buidhe Conail
11:48 - Y Fad Felen
15:53 - Pestis Flava

Sources (turn on captions):
Bartrum, P.C. (1993). A Welsh Classical Dictionary: People in History and Legend up to about A.D. 1000. The National Library of Wales.
[1] p.295-296
[2] p.503-504
[3] p.500

Cule, J. (1973). Pestis Flava: Y Fad Felen. Wales and Medicine.
[4] p.141
[5] p.142
[6] p.143
[7] p.144
[8] p.145
[9] p.146
[10] p.147
[11] p.148
[12] p.149
[13] p.150
[14] p.151
[15] p.152
[16] p.153
[17] p.154

Dooley, A. (2006). The Plague and Its Consequences in Ireland. Plague and the End of Antiquity.
[18] p.216
[19] p.217
[20] p.218
[21] p.219
[22] p.174

Gwenogvryn, J. (1893). The text of the Book of Llan Dav. Oxford.
[23] p.107
[24] BoL p131
[25] p.144

Llyfrgell Genedlaethol Cymru Archives.
[26] https://archives.library.wales/index.php/brut-y-brenhinedd-12

MacArthur, W. (1947). Famine Fevers in England and Ireland. Post-Graduate Medical Journal, (260). https://pmc.ncbi.nlm.nih.gov/articles/PMC2529527/
[27] p.285
[28] p.286

Snowden, J., Yarrarapu, S.N.S., Nguyen, A.D. and Oliver, T.I. (2025). Relapsing Fever. ncbi.nlm.nih.gov.
[29] https://www.ncbi.nlm.nih.gov/books/NBK441913/

[30] Wood, J. (2020). Y Fad Felen and Gwrach y Rhibyn: The Supernatural Female as Carrier of Disease in Welsh Tradition.

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Fortress Europe - Dan Bodan
Stuck In The Air - The Tower of Light
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Namaste by Audionautix is licensed under a Creative Commons Attribution 4.0 licence. https://creativecommons.org/licenses/by/4.0/ Artist: http://audionautix.com/
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Images of, and from:
Deganwy - Chris / The Site of Degannwy Castle: aerial 2015 / CC BY-SA 2.0 creativecommons.org/licenses/by-sa/2.0/ , via Wikimedia Commons
Llanrhos - NoelWalley, CC BY-SA 3.0 creativecommons.org/licenses/by-sa/3.0/ , via Wikimedia Commons
all other images are public domain, via the Rijksmuseum, Public Health Image Library, Minneapolis Institute of Art, Chicago Art Institute, Yale Center for British Art, the British Library