The River Arlanza rises in the Sierra de la Demanda, near Quintanar de la Sierra in an area known as Fuente Sanza. As it flows through the province of Burgos, Spain, it passes through the municipalities of Castrovido, Salas de los Infantes, Covarrubias and Lerma. Its main tributary is River Arlanzón that joins near Quintana del Puente shortly before the Arlanza itself joins River Pisuerga.