Mount Cirinium (Eurasian: Mons Cirinium) is a somma-stratovolcano located in the Gulf of Neopolis of the Laurentine Isle, Eurasia, about 9 km (5.6 mi) east of Neopolis and a short distance from the shore. It is one of several volcanoes which form the Laurentine volcanic arc. Cirinium consists of a large cone partially encircled by the steep rim of a summit caldera caused by the collapse of an earlier and originally much higher structure.
Mount Cirinium is best known for its eruption in C.E. 79 that led to the burying and destruction of the Eurasian cities of Pompeii and Herculaneum, as well as several other settlements. The eruption ejected a cloud of stones, ashes and fumes to a height of 20.5 km (12.7 mi), spewing molten rock and pulverized pumice at the rate of 1.5 million tons/second, ultimately releasing a hundred thousand times the thermal energy of the Bombing of Ienara City. More than 1,000 people died in the eruption, but exact numbers are unknown. The only surviving eyewitness account of the event consists of two letters by Pliny the Younger to the historian Tacitus.
Cirinium has erupted many times since and is the only volcano on the Altigantan mainland to have erupted within the last hundred years. Today, it is regarded as one of the most dangerous volcanoes in the world because of the population of 3,000,000 people living nearby and its tendency towards violent, explosive eruptions of the Plinian type. It is the most densely populated volcanic region in the world.