The Earthquake That Hit Pompeii Seventeen Years Before Vesuvius and Should Have Warned Everyone

A major earthquake struck the Vesuvian region of Campania on 5 February 62 AD. The two contemporary written sources — Seneca’s Naturales Quaestiones Book VI, composed within three years of the event, and a brief passage in Tacitus’s Annals — agree on the date and on the geographic extent. The earthquake caused substantial damage at Pompeii and significant damage at the neighbouring cities of Herculaneum and Naples; the rural Vesuvian villas were widely affected; specific Senatorial debate at Rome on whether to formally evacuate or rebuild the affected region is recorded by Tacitus.

The Senate voted to rebuild.

What the earthquake did

The 62 AD earthquake is now estimated by Italian seismologists at approximately magnitude 5.5 to 6.0 — substantial but not catastrophic by Mediterranean standards. Casualty figures were modest by the brutal standards of ancient earthquake history (Seneca records the death of an entire flock of 600 sheep at a single Pompeian property, but no comprehensive human mortality is given). The damage to standing structures was: most of the major public buildings of Pompeii — the Forum, the Temple of Jupiter, the Capitolium, the Basilica, the public baths — showed visible damage in the 79 AD archaeological record, and most of that damage matches the descriptions in Seneca and the architectural sequence the modern excavations have reconstructed.

Many of the buildings were still under repair seventeen years later when Vesuvius erupted. The reliefs from the household shrine of the Pompeian banker Lucius Caecilius Iucundus — preserved in the National Archaeological Museum of Naples — show specific buildings of the city collapsing during the earthquake, with the Temple of Jupiter (the Capitolium) shown with one corner already broken. The reliefs are dated to the period immediately after the earthquake and constitute the only known direct contemporary visual depiction of the event.

The magmatic interpretation

Modern volcanological interpretation reads the 62 AD earthquake as part of the precursor sequence of the 79 AD eruption. The earthquake’s depth and aftershock pattern (as best as those can be reconstructed from the literary and archaeological evidence) are consistent with volcano-tectonic seismicity — earthquakes generated by magma ascent rather than by tectonic-plate stress release. The pattern would substantively match what modern monitoring observes in the years preceding many active-volcano eruptions today: a major precursor earthquake, then a multi-year period of relative quiet during which magma chamber pressure continues to build, then the catastrophic eruption.

The Romans of 62 AD had no framework for reading any of this. Vesuvius had not erupted in living memory; the 79 AD eruption was the first historical Roman eruption from the volcano; the region’s standing perception of Vesuvius was substantively as a fertile but otherwise unremarkable mountain.

What Seneca thought

Seneca’s Naturales Quaestiones VI, written specifically in response to the 62 AD Pompeian earthquake, is one of the best-preserved scientific treatises of the Neronian period. Seneca proposed a substantively naturalistic theory of earthquakes — they were produced by underground air currents (spiritus) moving violently through subterranean caverns, occasionally bursting outward in seismic events. The framework was wrong in detail but substantively correct in its naturalistic orientation; it explicitly rejected the popular religious interpretation of earthquakes as divine punishment.

Seneca’s treatise did not connect the Pompeian earthquake to any potential future Vesuvian activity. The connection between earthquakes and volcanism would not be theoretically articulated in European natural philosophy until the work of Alfred Lacroix and the founding generation of modern volcanology almost 1,900 years later.

The seventeen years

The Pompeii of 79 AD that the eruption buried was a city in the middle of a reconstruction project. Many of the major public buildings still had visible earthquake damage; many private houses had been partially demolished and were being rebuilt; the marble cladding of the Forum had been removed for replacement and the underlying brick was exposed; new construction techniques (opus reticulatum, opus latericium) had been introduced in the rebuilding and characterise most of the post-62 AD Pompeian architectural fabric.

The 24 August (or, by recent re-dating from the carbonised food evidence, 24 October) 79 AD eruption found Pompeii in this in-between state. The plaster casts that Giuseppe Fiorelli’s 1860s excavations recovered include several figures who had been working on reconstruction at the moment of the eruption: a slave caught at a half-mixed plaster bucket, a workman with a trowel still in his hand, an architect with surveying tools.

The 62 AD earthquake had been the warning. Nobody was reading it.