Justinian Plague: Volcanic Winter or Comet Impact?

The Justinian Plague (541–542), named after emperor Justinian I (527-565), was a pandemic that afflicted the Byzantine Empire. The pandemic resulted in an estimated 25 to 50 million deaths in two centuries of its recurrence.

[Rabaul Volcano]

A global cooling in 536 AD, that preceded the plague, was possibly triggered by a major volcanic eruption that released immense amounts of ash and sulphur into the atmosphere. Two different volcanos are thought to be the culprit: Rabaul volcano (Papua New Guinea) and Lake Ilopango (El Salvador). Another theory is that the dust veil was due to a comet impact. Ice-core analysis of Greenland ice from between 533 and 540 AD do show high levels of tin, nickel and iron oxides from an extraterrestrial source in the dust layer[1].

The appearance of the dust veil in 536 AD had a major impact. Global cooling and colder summers caused crops to wither. Widespread famine ensued and this subsequently made the people of the time more susceptible to disease.

In 541 AD a mysterious illness began to appear on the outskirts of the Byzantine Empire. Victims were described as suffering from delusions, nightmares, fevers and swellings in the groin, armpits and behind their ears. The plague arrived in Constantinople, the capital of the empire, the following year. At its peak the plague was supposedly killing 10,000 people in Constantinople a day.

It had long been suspected that the Plague of Justinian was in fact bubonic plague, the cause of the infamous Black Death that also occurred in the 14th century. In 2012 it was finally confirmed that this was the case. A team of researchers analysed human remains from gravesites from the period and found the presence of Yersinia Pestis[1].

The Black Death was carried by rat fleas living on black rats. The infected rats and fleas travelled around the ports and trade routes of the Mediterranean via merchant ships.

The outbreak lasted less than 6 months in Constantinople but it is estimated that 40% of those living there died in that time period. The plague would reappear at periodic intervals over the next 300 years and it would eventually claim the lives of 25% of people living in the Mediterranean region. It is estimated that somewhere in the range of 25-50 million people died in total as a consequence of this catastrophic illness. The last recorded recurrence was in 750 AD, but by this time the outbreaks had become less virulent. The plague would then disappear from Europe completely until the 14th Century.

Whatever the cause of the Justinian Plague, be it volcanic or extraterrestrial, the course of human history was changed forever and Europe would not fully recover until the rise of the Renaissance.

[1] Rigby et al: A comet impact in AD 536? in News and Reviews in Astronomy and Geophysics - 2004. See here.
[2] Bos et al: Yersinia pestis: New Evidence for an Old Infection in PloS One - 201. See here.