sekhterion

The sekhterion, also known as a sector square or sectorial, is an ancient Greek surveying instrument used primarily for measuring angles and establishing right angles in land division and construction. Dating back to at least the 4th century BCE, it was a key tool in the field of geodesy, the science of measuring and mapping the Earth’s surface.

The sekhterion consisted of a square or rectangular base with a rotating arm attached at one corner. The arm was marked with angular divisions, allowing users to align it with celestial bodies, such as the sun or stars, to determine precise angles. By adjusting the arm to form a right angle with the base, surveyors could create perpendicular lines essential for laying out fields, roads, or buildings. Some versions incorporated a plumb bob or leveling mechanism to ensure accuracy in uneven terrain.

While the sekhterion shared similarities with other ancient surveying tools like the groma (used in Roman times), its design emphasized angular precision. It was particularly useful in agricultural contexts, where landowners needed to divide property fairly and efficiently. Archaeological evidence suggests its use in Greek colonies across the Mediterranean, though its exact construction varied by region.

Over time, the sekhterion was largely replaced by more advanced instruments, such as the astrolabe and theodolite, as mathematical and astronomical techniques evolved. However, it remains an important artifact in the history of surveying, illustrating early innovations in measurement and spatial organization. Modern historians and archaeologists study its remnants to understand ancient engineering practices and the development of cartography.