Did a catastrophic change in the climate bring about the dark ages? In the year 535-536 Byzantine historian Procopius recorded, "the sun gave forth light without brightness". Tree ring analysis show abnormally little growth in irish oak in 536 and another sharp drop in 542, similar patterns are recorded in Sweden, Finland and Sierra nevada In south america drought caused the collapse of the Teotihuacan empire. In china drought caused the tax base to collapse and destabilized the ruling powers In other parts of the world plagues broke out killing millions. The eruption of the indonesian volcano Krakatoa is the most probable trigger for all these events.