Europe · The early medieval west
Kingdom of Seisyllwg
drawn on the map AD 878–959
Seisyllwg comprised Ceredigion together with Ystrad Tywi (the valley of the Tywi), reputedly named after Seisyll ap Clydog, king of Ceredigion in the 7th or early 8th century, its traditional founder (though the timing of its emergence is unclear).
- Shown on the map
- AD 878–959
- Peak area
- 18k km²
- Region
- Europe
Names and origin
Seisyllwg comprised Ceredigion together with Ystrad Tywi (the valley of the Tywi), reputedly named after Seisyll ap Clydog, king of Ceredigion in the 7th or early 8th century, its traditional founder (though the timing of its emergence is unclear).
Hywel Dda and Deheubarth
In the 10th century Seisyllwg became the power-base of Hywel Dda ("Hywel the Good," d. 949/950), grandson of Rhodri Mawr. Hywel became sole ruler of Seisyllwg on his brother Clydog's death in 920 and, by merging Seisyllwg with the neighbouring Kingdom of Dyfed (which he acquired by marriage to Elen ferch Llywarch), created the new kingdom of Deheubarth, with its base at Dinefwr. Hywel came to rule most of Wales, made a pilgrimage to Rome (928), was the only Welsh ruler to issue his own coins, and attended Æthelstan's court as a witness to charters. He is celebrated above all for the Laws of Hywel Dda (Cyfraith Hywel), the native Welsh legal tradition traditionally ascribed to his codification; the actual surviving texts date from later centuries (some 30 medieval manuscripts, in Welsh and Latin), so the precise attribution to Hywel is a matter of tradition rather than contemporary record.
Common questions
- What was the Kingdom of Seisyllwg?
- Seisyllwg comprised Ceredigion together with Ystrad Tywi (the valley of the Tywi), reputedly named after Seisyll ap Clydog, king of Ceredigion in the 7th or early 8th century, its traditional founder (though the timing of its emergence is unclear).
- When is the Kingdom of Seisyllwg shown on the map?
- The border data draws the Kingdom of Seisyllwg AD 878–959. The source samples borders at fixed dates, so a span can begin late or run on past the end.
- How large was the Kingdom of Seisyllwg?
- At its greatest extent drawn on this map, the Kingdom of Seisyllwg covered about 18,000 km². That is the largest area the border data gives it across the years it is drawn, not necessarily its greatest extent in history.
Sources
This compendium cites its sources once for the whole document rather than per territory. Its bibliography names the English Wikipedia articles for each kingdom as the primary basis, with Encyclopædia Britannica, the World History Encyclopedia, national heritage bodies (Historic Environment Wales and Scotland, the Clwyd-Powys Archaeological Trust), museum sources and the Dictionary of Irish Biography, read against the Anglo-Saxon Chronicle, Bede and the Irish annals with their own biases. The article this entry is anchored on:
- Wikipedia — Seisyllwg en.wikipedia.org/wiki/Seisyllwg
This entry was last updated .
This entry was researched and drafted with AI from the sources above, and has not been reviewed by a historian. How entries are made
Text available under CC BY-SA 4.0: reuse it with a credit to The World Through Time and a link to this page. Passages drawing on the Wikipedia articles listed above are also licensed CC BY-SA 4.0 by their contributors.
Border geometry for the map itself comes from Cliopatria v0.12 (Seshat Global History Databank, CC-BY-4.0).
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