This roughly made groma was found during an excavation in the Fayum Province of Egypt in 1899. Early surveyors' instruments such as this were useful only on flat terrain and for setting a limited range of angles. With the groma, distant objects were marked out against the position of the stones in a horizontal plane. The groma is thought to have been used to set out the lines of roads at right angles in the 1st and 2nd centuries BC.
© Science Museum / Science & Society Picture Library