Historian Michael McCormick of Harvard University and a group of researchers decided to find out what really happened in 536 AD. Scientists based on the records of those years, in particular, the Byzantine historian Procopius of Caesarea, who wrote: “And this year the greatest miracle happened: all year the sun emitted light like the moon, without rays, as if it had lost its power and ceased, as before, shine clean and bright. From the time it began, neither war, nor a pestilence, nor any other disaster bringing death has ceased among people. It was the tenth year of Justinian's reign."
According to McCormick, those years can be safely called the worst period known in history for life. There was a sharp cooling - that decade in Europe was the coldest in the last 2000 years. All of Europe, the Middle East and some regions of Asia were enveloped in fog - due to poor harvests, famine began, and from 536 to 539 there was a shortage of bread. In 541, an epidemic of the bubonic plague began. The general decline lasted for about 100 years, until 640.
What led to such a sharp drop in temperature and the formation of a mysterious fog? Scientists took samples of ice and snow from mountain glaciers in the Alps in Switzerland - as a rule, changes in the composition of the atmosphere leave "traces" in the layers of snow. At the University of Maine, an analysis was carried out, which revealed samples dating from the spring of 536 - microscopic particles of volcanic glass were found in them. Further investigation revealed that the particles originate from Iceland. In 536, there was such a powerful volcanic eruption that a cloud of ash literally covered the sky in the Northern Hemisphere. Subsequent eruptions in 540 and 547 complicated the situation.