For each revolution a pin on the axle engaged a 400-tooth cogwheel thus turning it one complete revolution per mile. The odometer of Vitruvius was based on chariot wheels of 4 Roman feet (1.18 m) diameter turning 400 times in one Roman mile (about 1,480 m). Some researchers have speculated that the device might have included technology similar to that of the Greek Antikythera mechanism. 192 AD), although after this point in time there seems to be a gap between its use in Roman times and that of the 15th century in Western Europe. The machine was also used in the time of Roman Emperor Commodus (c. Hero of Alexandria (10 AD – 70 AD) describes a similar device in chapter 34 of his Dioptra. Since these minor discrepancies can be adequately explained by slight changes in the tracks of roads during the last 2300 years, the overall accuracy of the measurements implies that the bematists already must have used a sophisticated device for measuring distances, although there is no direct mention of such a device.Īn odometer for measuring distance was first described by Vitruvius around 27 and 23 BC, although the actual inventor may have been Archimedes of Syracuse (c. From the nine surviving bematists' measurements in Pliny's Naturalis Historia eight show a deviation of less than 5% from the actual distance, three of them being within 1%. For example, the section between the cities Hecatompylos and Alexandria Areion, which later became a part of the silk road, was given by Alexander's bematists as 575 Roman miles (529 English miles) long, that is with a deviation of 0.2% from the actual distance (531 English miles). However, the high accuracy of the bematists's measurements rather indicates the use of a mechanical device. 336-323 BC) as by his bematists Diognetus and Baeton.
Both authors list the distances of routes traveled by Alexander the Great (r. Possibly the first evidence for the use of an odometer can be found in the works of the ancient Roman Pliny (NH 6. Reconstruction of Hero's odometer, 1st century AD, Alexandria, Thessaloniki Science Center and Technology Museum
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