Astride the provinces of Palencia, Valladolid, Zamora, and León, the Tierra de Campos is one of the most emblematic districts of Castilla y León. It is considered an example of the extensive plains of the northern plateau which are green in spring, ochre in autumn, white in winter, and golden in summer. It has been one of the main cereal districts of Spain since the Roman Hispania. As a result it is known as “the granary of Spain”. It contains the largest concentrations of great bustards in the world. The wetlands of the Laguna de la Nava (Palencia province) and the Lagunas de Villafáfila (Zamora province) are key bird migration spots.