There are 44 municipalities: [1] The waters of the river Arlanza originate in the pines forest of Quintanar de la Sierra and flow from East to West.

This is due to the fact that the land descends from heights such as Peñas de Cervera (Mount Valdosa, 1412 m) and The Mamblas (1372 m) to the border with Palencia.

Freeways are acceptable: from North to South crosses the national N-I from Madrid to Irun and from west to east the N-622 from Lerma to Palencia.

The Arlanza zone was repopulated mainly by Astur, Cantabri, Visigothic and Mozarab peoples in the mid-ninth century, after the border of the County of Castile and the Kingdom of Córdoba reached the river Duero.

Villa Rachela de Covarrubias, an artistic historic place and the old capital of a religious state; Villa Ducal de Lerma, which was turned by the eponymous Duke into one of the most beautiful urban sets in Spain; Santa María del Campo, the old capital of Betherías.