Pompeii’s famous body casts were made by filling voids in volcanic deposits.

Volcanic deposits hardened around victims, preserving an external mould even after much of the biological material inside had decayed.

Archaeologists introduced liquid plaster into suitable cavities and removed the surrounding deposits after it set, revealing forms that excavation alone might have destroyed.

The results combine ancient evidence with a modern recording technique, so they must be understood as both records of people and products of archaeological intervention.

In 79 CE, the eruption of Mount Vesuvius buried Pompeii beneath volcanic material. The event killed inhabitants and covered houses, streets and objects. Different phases of the eruption produced different burial conditions, so not every victim's remains survived in the same way. The familiar casts represent a particular form of preservation, not the universal condition of everyone who died in the city.

Where deposits enclosed a body and retained its shape, the surrounding material could function as a natural mould. Over time, soft tissues and other organic material deteriorated. A cavity remained where the body had been, sometimes retaining details of clothing and posture. Bones could remain inside. The critical survival was therefore partly an absence: a shaped space within the hardened deposit.

Excavating straight through such a cavity would risk collapsing or destroying its outline. The casting method instead gives the space a solid form before the surrounding material is removed. Liquid plaster introduced into the void fills the available contours. Once the plaster has hardened, excavation can expose the cast, making visible details that otherwise existed only on the cavity's inner surface.

Giuseppe Fiorelli developed the famous application of this method at Pompeii in 1863. That date belongs to the history of excavation, almost eighteen centuries after the eruption. It is not the date when the victims were buried or when the cavities first formed. The casts connect those separate moments: ancient burial conditions created the moulds, and modern archaeologists supplied the material that made them visible.

Describing the casts as bodies turned to stone is therefore inaccurate. Their visible external form is largely supplied by plaster or another casting material. At the same time, calling them merely statues would also be misleading, because their contours derive from archaeological cavities rather than an artist's free invention. Some casts incorporate skeletal remains, which means they can also contain genuine human material.

The technique was not limited to people. Pompeii's archaeological park explains that casts could also record perishable things such as wooden furnishings, doors and windows. In each case, the same basic principle applies: something decays, the surrounding deposit retains its impression, and an introduced material reproduces that impression. This makes negative spaces a valuable source of information about otherwise vanished objects.

The casts can be emotionally powerful, but posture alone does not establish a person's identity, relationship to nearby victims or exact final thoughts. Interpretation requires the find location, surviving remains and other evidence. Respectful presentation also matters: these forms record real deaths rather than fictional scenes. Their scientific importance and their human significance are inseparable, even though the material most visible to a visitor is modern.

A cast is not a person turned into stone. It is a later material introduced into a space that retained a body's form after soft tissues decayed. The distinction is essential to understanding both what visitors see and the archaeological process that produced it.

The technique also connects human remains with the surrounding volcanic deposits. Preservation depended on the relationship between a body and the material enclosing it. The resulting shape is powerful evidence, but it does not automatically establish a name, occupation, or complete final story.