About 20 kilometers southeast of Rome is the Alban Hills Volcanic Complex, a dormant volcano which last erupted about 37,000 years ago. To the Romans it was known as Albanus Mons. It is thought there is a slowly growing spherical magma chamber underneath the complex which will eventually erupt again. But what if it had grown somewhat faster? I offer the following scenario...
On July 21, 102 A.D., the Emperor Trajan is away in Dacia, fighting the First Dacian War. The people of Rome go about their business, unaware that, in the Albanus Mons, a disaster is in the making. The first inkling they have of trouble occurs when the ground in the center of the complex begins to bulge upward noticeably, and there is an earthquake, damaging a number of buildiings in Rome. Some people (about 1/10 of the population) leave the city. The bulge continues to grow over the next couple of days, then on July 23, there is a catastrophic explosion. An eruption basically equal in scale to the 1625 B.C. eruption of Santorini takes place, with effects very similar to those of the Santorini eruption. Rome is effectively wiped off the map, along with a number of surrounding towns, buried, like Pompeii, under tons of volcanic ash. Most of central Italy is laid waste by the explosion, by fires caused by the eruption, and by earthquakes accompanying the explosion. Huge plumes of ash are cast into the atmosphere, leading to colder temperatures across the Northern hemisphere for the next decade. There are crop failures in many places as a result, especially in Italy and Gaul, but also in many other places as well. A huge (100 ft or more high) Tsunami wave sweeps outward from the coast, hitting Sardinia, Sicily, Spain, and North Africa within 24 hours.
Can the Emperor Trajan pick up the pieces and save his Empire, or will the loss of the imperial center and the attendant environmental effects cause a system-wide collapse?