The excavation of an ancient rock shelter in northern Spain has yielded evidence of 5,000-year-old livestock pens. The ancient structures offer some of the earliest evidence of the use of rock walls to secure livestock in the region.

Scientists have previously documented livestock enclosures among ancient settlements of Sierra de Cantabria, the mountain range in the Spanish province of Álava, but this is the first time researchers have used a combination of geological and paleobotanical evidence to do so.

The research team -- including scientists from the University of the Basque Country and the University of Barcelona -- confirmed the purpose of the rock shelter through analysis of charcoal, pollen, seeds and other plant remains.

Scientists hope continued analysis of the site will illuminate the nature of the early agropastoral groups that settled and migrated across the Basque Country several thousand years ago during the Chalcolithic, or Copper Age.

The time period marks a transitional phase in European prehistory, when hunter-gatherer groups came into contact with migrating people from the east who brought traditions of subsistence farming.

The sedimentary and paleobotanical findings suggest the rock shelter was not in continual use but was likely used for brief periods of time as herders followed resources across the region. It's possible a more permanent settlement existed nearby.

"We also know thanks to the microscopic study of the sediments that every now and again they used to burn the debris that had built up, probably to clean up the space that had been occupied," researcher Ana Polo-Diaz, an archaeologist with the University of the Basque Country, said in a news release.

Ancient pollen suggests the area once featured a forest of hazelnut and oak trees. The trees likely provided wood for shelter for the human travelers and food for animals.

Researchers published their latest findings in the journal Quaternary International.