Around 400 BCE, people across northern Iberia left their fortified settlements and built new ones. A new study shows the move came in two stages with very different speeds. The old settlements emptied within a few decades. The new ones took far longer to spread.
Samuel Nión-Álvarez of INCIPIT-CSIC built the timeline from 272 radiocarbon dates taken at 109 archaeological sites. The sites sit in five areas: the Atlantic region, the western and eastern Cantabrian regions, and the western and eastern Northern Plateau. He used Bayesian models and other statistical tests to compare when sites were abandoned with when new ones began.
The timing matters because Europe went through big social change around 400 BCE. Some scholars call this period the Crisis of the 400s. Climate shifts, migration and conflict have all been blamed, but nobody has settled on a cause. Changes also looked different from place to place. Northern Iberia works well as a test case because of its many kinds of settlements and plenty of radiocarbon dates.
The decline started in the western Cantabrian region. The first sites there were left behind in the late sixth and early fifth centuries BCE. The trend then moved to the Atlantic region and the western Northern Plateau. By the last decades of the fifth century BCE, people had abandoned sites at both the western and eastern edges of the study area.
Most Early Iron Age settlements stood empty in under a hundred years. No single date marks the break. Each region went through its own sharp change over a few decades, and the older and newer phases barely overlapped. In a few places, people came back to abandoned sites later.
Rebuilding ran at a slower pace. New settlements began to appear in the early fourth century BCE, first in the western Cantabrian and Atlantic regions. Larger settlements followed. Many had defensive walls and sat closer to good farmland. They spread over a much longer stretch of time and moved across the Northern Plateau. In the far east, fortified settlements became common only around the start of the third century BCE.
The shift left smaller marks in the ground too. Short-term camps, ritual sites and burials show up in the record, mostly in the Atlantic region. Their dates overlap with the fading of the older settlements. Other parts of the Cantabrian coast have too little evidence to tell whether the same thing happened there.
People did more than change addresses. Late Iron Age settlements were bigger and more complex, and some regions saw wider gaps between rich and poor. This new pattern lasted until Roman times. Nión-Álvarez links the changes to a broad reorganization of communities. He also points out the pace and form differed from region to region.
The study doesn’t say why people left. War, population growth and shifting social structures are all on the table. The early decline of hillforts in Asturias is still a puzzle. What the work gives researchers is a firm timeline for each stage, so they can test possible causes against solid dates.
The paper also offers a method others could reuse. The method combines radiocarbon models with estimates of how much date ranges overlap. This shows whether events happened together, one after another, or at separate times in different regions. Archaeologists could apply the same approach to other fast changes in European prehistory.