The founder of the ducal branch was Count Siegfried I (1010–1065), a Ripuarian Frank by birth and retainer of the Salian emperor Conrad II.

By his marriage to Richgard, daughter of one Count Engelbert of the Bavarian Sieghardinger noble family, he became heir to large territories in Carinthia and Tyrol.

When the ducal House of Eppenstein finally became extinct in 1122, Siegfried's grandson Henry inherited the title and became the first Sponheim Duke of Carinthia as well as Margrave in the Italian March of Verona.

The Sponheim dukes tried to consolidate their possessions by being loyal liensmen of the Imperial House of Hohenstaufen, they nevertheless had to struggle with reluctant local nobles like the Carinthian Ortenburger.

However, as he outlived his children, he bequested his Carinthian and Carniolan lands to his Přemyslid cousin King Ottokar II of Bohemia according to a secret inheritance agreement of 1268.