Poza de la Sal

Human presence around Poza de la Sal stretches back to the Neolithic, evidenced by megalithic structures at Altotero, Poza I, and the Túmulo del Hoyo. By the Bronze and Iron Ages, a settlement known as Salionca, belonging to the Autrigones people, occupied the site of what is now the Castellar and the ground around the castle.

The town's strategic importance grew sharply under Roman rule, when it became one of the peninsula's main centres of salt production — a commodity so valuable to food preservation that it was used as a form of payment, giving rise to the word salary.

Toward the end of the ninth century, Count Diego Rodríguez Porcelos repopulated Poza and built the castle to defend the new frontier. This happened in the same period as the construction of Pancorbo castle and the founding of Burgos in 884.

When the Old Regime ended, Poza was constituted as a constitutional municipality within the partido of Briviesca, in the region of Castilla la Vieja, with a population of 2,006 at that time.

In more recent history, Poza had its own railway station on the Santander–Mediterranean line, which ran between 1929 and 1985. The old track has since been converted into a greenway, the vía verde, now open to walkers and cyclists.

Poza de la Sal's old town was declared a protected Historic-Artistic Ensemble on 12 November 1982, and the designation reflects how much has survived. The medieval walls still stand largely intact — five metres high and two metres thick — and the street plan inside them remains essentially medieval: narrow, steep lanes lined with stone houses bearing heraldic crests, and timber-framed buildings with plaster infill.

Three gateways pierce the walls: the Puerta del Conjuradero, the Puerta del Ayuntamiento, and the Puerta de las Eras. Inside, the church of San Cosme y San Damián anchors the old town, with the traditional market square, the Plaza Vieja, opening directly below it. The town hall stands beside the church, and in front of it a newer square opens onto wide views over the comarca of La Bureba — hence the town's nickname, the Balcony of La Bureba. Above the streets, a tower is all that remains of the palace of the Marquises of Poza; higher still on the hill stands the castle.

The town's wealth and its defences both grew from salt. The salt pans at Poza, alongside those at Añana in Álava, were the principal ones in northern Iberia. Spring water was channelled through aqueducts to wooden and stone platforms called granjas, where it was spread into rectangular evaporation beds, or eras. The dried salt was then stored in rain-protected deposits called terrazos. A pumping system also pushed water underground to increase yields. Philip II declared a royal monopoly on salt in 1564, which lasted until 1888. The last era closed in 1974, ending production entirely.

In 2001 the salt pans were declared a Bien de Interés Cultural. Two years later, the former Casa de Administración de las Salinas Reales became an interpretation centre on the history of salt, and some of the eras and brine pools were restored for visitors.

Down near the river, the complex known as Fuente Buena or Fuente Vieja — a group of freshwater springs feeding old wash houses, animal troughs, and a leather-tanning works — dates from the same era, though with Roman traces beneath it.