Siero borders on the municipalities of Gijón to the north, Langreo and San Martín del Rey Aurelio to the south, Llanera and Oviedo to the west, and Sariego, Nava, and Bimenes to the east.

[3] On the site prior to that date there was a hostel which provided accommodation and sustenance for pilgrims travelling the Way of St. James (Camino de Santiago), en route to or from Santiago de Compostela.

The charter allowed the formation of the town, imposed an annual tax on the inhabitants to be paid to the crown, and granted them a license to hold a weekly market in the town square, Plaza les Campes.

This market, a feature of Pola de Siero which continues, every Tuesday, to this day, was the decisive factor in the development of the town.

[4] With the market, the town became the focal point of a large rural area of fertile land, and thereafter other commercial and administrative functions followed.