Vitruvius
Vitruvius ( ; ; –70 BC – after ) was a Roman architect and engineer during the 1st century BC, known for his multi-volume work titled . As the only treatise on architecture to survive from antiquity, it has been regarded since the Renaissan ...
in Book VIII of the ''
De architectura
(''On architecture'', published as ''Ten Books on Architecture'') is a treatise on architecture written by the Ancient Rome, Roman architect and military engineer Vitruvius, Marcus Vitruvius Pollio and dedicated to his patron, the emperor Caesa ...
'', was used to measure horizontal planes and was especially important in the construction of aqueducts.
Similar to modern
spirit level
A spirit level, bubble level, or simply a level, is an Measuring instrument, instrument designed to indicate whether a surface is Horizontal plane, horizontal (level) or vertical direction, vertical (plumb-bob, plumb).
Two basic designs exis ...
s, the chorobates consisted of a beam of wood 6 m in length held by two supporting legs and equipped with two plumb lines at each end. The legs were joined to the beam by two diagonal rods with carved notches. If the notches corresponding to the plumb lines matched on both sides, it showed that the beam was level. On top of the beam, a groove or channel was carved. If the condition was too windy for the plumb bobs to work effectively, the surveyor could pour water into the groove and measure the plane by checking the water level.
Isaac Moreno Gallo's interpretation of the chorobates
Isaac Moreno Gallo, a Technical Engineer of Public Works specialized in Ancient Rome's
civil engineering
Civil engineering is a regulation and licensure in engineering, professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads ...
, claims that the present-day representation of the chorobates (in a table-like shape) is mistaken due to a misinterpretation derived from an incorrect translation of the Latin term "ancones" used by
Vitruvius
Vitruvius ( ; ; –70 BC – after ) was a Roman architect and engineer during the 1st century BC, known for his multi-volume work titled . As the only treatise on architecture to survive from antiquity, it has been regarded since the Renaissan ...
.
''"...ea habet ancones in capitibus extremis aequali modo perfectos inque regulae capitibus ad nomam coagmentatos..."''
In this context, "ancones" could be translated as "limbs" (extremidades) or "arms", but also as "ménsulas" (brackets or corbels). According to Isaac Moreno, this vertical design is way more efficient when it comes to optical leveling and makes more sense from a topographer's point of view. Furthermore, it preserves the original length described by Vitruvius (20 feet or 5.92 meters) that the table-like chorobates versions persistently seem to ignore.
This "vertical" chorobates was indeed the predominant interpretation of the chorobates in the oldest representations recorded: 1547's engravings included in Jean Goujon's translation of Vitrubius works into French. Or 1582's Miguel de Urrea's first edition of Vitrubius works, this time in Spanish. And few years later, when Juan de Lastanosa published “The Twenty-One Books of Engineering and Machines" of Gianello della Torre”.
All three of them consistently represented the chorobates in a very similar way, until 1673
Dioptra
A dioptra (sometimes also named dioptre or diopter, from ) is a classical astronomical and surveying instrument, dating from the 3rd century BC. The dioptra was a sighting tube or, alternatively, a rod with a sight at both ends, attached ...
Odometer
An odometer or odograph is an instrument used for measuring the distance traveled by a vehicle, such as a bicycle or car. The device may be electronic, mechanical, or a combination of the two (electromechanical). The noun derives from ancient Gr ...