The Duchy of Lower Lorraine encompassed part of modern-day Belgium and the Netherlands. It was closely tied to the Duchy of Upper Lorraine and the County of Boulogne. It was a major participant in the First Crusade; Godfrey of Bouillon later became the first King of Jerusalem (although he actually took the title "Defender of the Holy Sepulchre").
Dukes of Lower Lorraine
County of Bouillon
Within Lower Lorraine was the County of Bouillon; its counts were often simultaneously Dukes of Lower Lorraine, and after the death of Godfrey of Bouillon the County passed through numerous hands throughout the centuries.
Counts of Bouillon