Iron Age Cold Epoch

The Iron Age Cold Epoch (also referred to as Iron Age climate pessimum or Iron Age neoglaciation) was a period of unusually cold climate in the North Atlantic region, lasting from about 900 BC to about 300 BC, with an especially cold wave in 450 BC during the expansion of ancient Greece. It was followed by the Roman Warm Period (250 BC – 400 AD).

...
Wikipedia