The eruption of Hekla, Iceland, at about 1150 BC and consequent climatic worsening is detectable through Greenland ice-cores, the bristlecone pine sequence, and the Irish oak sequence. The construction of Haughey's Fort, Armagh, at about this time also supports evidence of scarce resources. Numerous catastrophic or violent events from the Caspian Sea to Norway also center on this period. Questions nonetheless remain: do the tree rings merely provide an anchor-date to which approximately dated events can be manipulated, and was Hekla 3 the sole cause of climatic worsening in mid-12th century? All the disciplines need to refine their dating.