The Counts of Louvain (French) or of Leuven (Dutch) were the rulers of the County of Louvain. Near the end of the tenth century, the County of Louvain emerged when granted to Lambert I of the House of Reginar 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 Louvain 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.