Near the end of the 10th century, the County of Leuven emerged when granted to Lambert I by the German Emperor. Originally limited by the rivers Demer, Dijle and Velp, that is more or less the region known today as Hageland, the County of Leuven rapidly increased in size and power. After his marriage with Gerberga, the daughter of the Duke of Lower Lorraine, Lambert I incorporated the County of Brussels; in 1013, Lambert I annexed the Duchy of Bruningrode, located around Tongeren.
They acquired great influence in the Holy Roman Empire and acquired more titles over time. In 1183, they were created Dukes of Brabant. The county of Leuven was absorbed into the duchy of Brabant.
From 1183 onwards the titles of Count of Leuven, Count of Brussels and Landgrave of Brabant were merged in the title of Duke of Brabant and used as appanages.