The groma was the principal surveying instrument of the Roman agrimensores, the land surveyors. The instrument itself was simple in design, crossed arms resting on a bracket and attached to a vertical staff. The four arms each had a cord with a hanging plumb bob. It was designed to survey straight lines and right angles. On the right is a drawing of a replica of a groma now in the Science Museum, London. The original metal parts were found in the Workshop of the surveyor Verus at Pompeii, and are now in the Museo Nazionale, Naples. Click on the plumb bobs or the pointed end of the staff to see photographs of the original parts.
are fortunate to have the tombstone of a Roman surveyor with a sculpted
relief, figure to the left, which depicts certain attributes of his
profession. It is the tombstone of Lucius Aebutius Faustus, of the first
century B.C. and is in the Museo Civico at Ivrea in Northern Italy.
Lucius Aebutius Faustus, freedman of Lucius Aebutius, of the tribe of Claudia, surveyor, sevir, erected this monument while still alive for himself and his wife Aria Aucta freedwoman of Quintus Arrius, and their children, and the freedwoman Zepyra.
The component parts of the sculptural relief are the following: In the pediment are a shield and spears. Beneath the inscription is a dismantled groma. Above this are the symbols of a sevir, two fasces and between them a low seat.
These plumb-bobs are examples of what
Roman carpenters, bricklayers, and surveyors used to trace vertical
lines and to determine horizontal planes. Plumb bobs are usually conical
and are either made of bronze or iron.
The point (to the right), usually made of bronze, was placed on the end of a staff to secure the groma in its position before surveying. It is possible that this example was used either on a groma or on a measuring staff.