Most Aquitainian counts elected Pepin II as their king, but Emperor Louis the Pious, urged by his wife Judith, redivided his vast realm at Worms in May 839, granting all of Aquitaine, Gascony, Septimania, and the Hispanic March to his youngest son, Charles the Bald.
Seguin was appointed dux Wasconum by Louis the Pious—that is, duke of the march guarding the frontier with the Gascons, led by Sancho, most probably a Basque himself.
Historian Ferdinand Lot supposed that Sancho was even nominated as duke at Limoges or Orléans by Charles the Bald in that year.
[3] With his brother-in-law Emenon, Count of Périgord, the husband of his sister Sancha, Sancho was captured by the dissident Moorish chieftain Musa.
Charles negotiated their release and in turn Sancho handed over Pepin II when the latter took refuge in Gascony in September 852.