Scientists think they have found the volcano responsible for a huge eruption that occurred in AD1257.
The event was so large its chemical signature is recorded in the ice of both the Arctic and the Antarctic.
European medieval texts talk of a sudden cooling of the climate and of failed harvests.
A study published in the PNAS journal has established the eruption was the Samalas volcano on Lombok Island, Indonesia.
The BBC reports an estimated 40 cubic-km of rock was discharged from the volcano. Little remains of the original mountain structure - just a huge crater lake.
"The evidence is very strong and compelling," Professor Clive Oppenheimer of Cambridge University told the BBC. He and his colleagues say only Samalas can "tick all the boxes".
In comparison with recent catastrophic blasts, the researchers believe Samalas was at least as big as Krakatoa (AD1883) and Tambora (AD1815).