From the Wikipedia page [1]
The province of Burgos is a province of northern Spain, in the northeastern part of the autonomous community of Castile and León. It is bordered by the provinces of Palencia, Cantabria, Vizcaya, Álava, La Rioja, Soria, Segovia, and Valladolid. Its capital is the city of Burgos.
The Cartularies of Valpuesta from the monastery Santa María de Valpuesta, in Burgos, are considered to be the oldest known documents containing words written in the Spanish language.