Pre-Roman Iron Age

The archaeological record for the 5th-3rd centuries BC is rich in rural settlements and remains of agriculture but very poor in artefacts. This is mainly due to extremely austere burial customs where few people received formal burial and those who did got little in the way of grave goods. There is little indication of any social stratification. Bronze importation ceased almost entirely and local iron production started in earnest.

A typical Clearance cairn from Eglinton Country Park in Scotland, The climate took a turn for the worse, forcing farmers to keep cattle indoors over the winters, leading to an annual build-up of manure that could now for the first time be used systematically for soil improvement. Fields were however still largely impermanent, leading to the gradual coalescence of vast systems of sunken fields or clearance cairns where only small parts were tilled at any one time. From the 2nd century BC onward, urn cremation cemeteries and weapon burials with various above-ground stone markers appear, beginning a monumental cemetery record that persists unbroken until the end of the Iron Age. Cemeteries of these roughly 13 centuries are by far the most common type of visible ancient monument in Scandinavia. The reappearance of weapon burial after millennium's hiatus suggests a process of increased social stratification similar to the one at the beginning of the Bronze Age.

References: Wikipedia