Pre-history (Paleolithic, Neolithic, the Copper Age and the Second Iron Age)
This area has been continually occupied since the Late Neolithic period (between 4 and 5,000 years BC) as confirmed by archaeological remains found in different locations around the valley. With the arrival of a new historical period - the Holocene - and the more temperate climate associated with it, human groups began new ways of occupying the land. In our lands, hunting and gathering would continue to be a force in the economy although a component of agro pastoral activity was added to these ancient occupations, based on extensive and itinerant agriculture in the most fertile areas (i.e. the valley bottom) and a wide-ranging animal husbandry necessitating frequent displacement of human groups. This explains the transient nature of early settlements in which shelters were constructed using perishable materials thus making their preservation to the present day impossible. In contrast to the scarcity of dwellings, the remains of which can hardly be detected, human groups of those times developed an original architecture for funeral purposes based on huge collective tombs or megaliths. In the Mena Valley diverse megalithic structures have been detected including corridor sepulchres (in Villasuso), dolmens (in Santa Olaja, Angulo) and simple chambers below tumuli (in the Ordunte Mountains).
The period between 2900 – 2000 BC saw a new stage in the evolution of human co-operatives in the area characterised, among other things, by great advances in the process of sedentarisation and the arrival of copper metallurgy. Attributed to this period, known as the Copper Age or Calcolithic, is a major settlement in the environs of the Ordunte Reservoir consisting of various funeral tumuli and an extensive open-air living area in which more than twenty fireplaces remain. The two archaeological zones are side by side indicating a strong relationship between ground dedicated to the dead and that of the living. Archaeological digs undertaken in 1991 brought to light lithic (stone) tools such as arrowheads with incipient tails, geometric microliths and pieces of axe all associated with this era.
The archaeological sequence corresponding to pre-history in the Mena Valley ends with a settlement found on Mount Socueto, near present-day Opio. The discoveries include a fort from the Second Iron Age (around 4 – 1 BC) inhabited in its day by the ‘autrigones’, an Indo-European people who established themselves the length and breadth of a strip of land reaching from the Cantabrian coast to the county of La Bureba, including the modern day counties of Merindades and the Valle de Mena. The influence of this influx of Indo-Europeans on the indigenous population lead to a lifestyle and material culture amply illustrated in the Opio settlement and the findings linked with this fortified dwelling.
The entire fort settlement, except the north flank which has natural protection, is surrounded by a double wall and on the inside artificial, man-made terracing and mounds of stone probably corresponding to the inhabitants cabins can be seen.