Bematist

Bematists or bematistae (Ancient Greek βηματισταί, from βῆμα bema 'pace'), were specialists in ancient Greece who were trained to measure distances by counting their steps.

Measurements of Alexander's bematists

Bematists accompanied Alexander the Great on his campaign in Asia. Their measurements of the distances traveled by Alexander's army show a high degree of precision to the point that it had been suggested that they must have used an odometer, although there is no direct mentioning of such a device:

"The overall accuracy of the bematists’ measurements should be apparent. The minor discrepancies of distance can be adequately explained by slight changes in the tracks of roads during the last 2,300 years. The accuracy of the measurements implies that the bematists used a sophisticated mechanical device for measuring distances, undoubtedly an odometer such as described by Heron of Alexandria."[1]

The table below lists distances of the routes as measured by two of Alexander's bematists, Diognetus and Baeton. They were recorded in Pliny's Naturalis Historia (NH 6.61–62). Another similar set of measurements is given by Strabo (11.8.9) following Eratosthenes.[2]

Pliny 6.61–62 Strabo 11.8.9 Actual distance
Route Milia passuum 1) English miles Deviation Stadia 2) English miles Deviation English milesRoute
Northern Caspian Gates – Hecatompylos — — — 1960 225 0.8% 227main road
Southern Caspian Gates – Hecatompylos 133 122 2.4% — — — 125main road
Hecatompylos – Alexandria Areion 575 529 0.4% 4530 521 1.9% 531Silk Route
Alexandria Areion – Prophtasia 199 183 3.2% 1600 184 2.6% 189Herat-Juwain
Prophtasia – Arachoti Polis 565 520 1% 4120 474 9.7% 525Juwain – Kelat-i-Ghilzai
Arachoti Polis – Hortospana 250 230 0.4% 2000 230 0.4% 231main road Kelat-i-Ghilzai – Kabul
Hortospana – Alexandria ad Caucasum 50 46 2.1% — — — 47Kabul – Begram
Alexandria ad Caucasum – Peucolatis 237 218 3.2% — — — 211Begram – Charsada
Peucolatis – Taxila 60 55 20% — — — 69Charsada – Taxila
Taxila – Hydaspes (Jhelum) 120 110 4.8% — — — 105Aurel Stein’s route
Alexandria Areion – Bactra – Zariaspa3) — — — 3870 445 1.6% 438via Kala Nau, Bala Murghab, Maimana and Andkhui
Average 4.2% 2.8%
Median 2.8% 1.9%

Notes:
1) 1 mille passus = 1,480 meters or 1,618.5 yards
2) 1 Attic stadion = 606’10’’
3) The route is not recorded to have been followed by Alexander himself.

Addenda: Leaving out the highest outlier each, the average deviation of the rest of the bematists's measurements would be 1.9% with Pliny and 1.5% with Strabo at a measured distance of 1,958 respectively 1,605 miles.

List of bematists
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gollark: I have Discord open in multiple browser tabs, and *this* one works fine, but the others are disconnected, weirdly.
gollark: Apparently no.
gollark: Google almost certainly handles most of the ads *automatically*, though you'd really think they could filter for keywords.
gollark: It says it's already claimed anyway.

See also

References
  1. Engels 1978, p. 158
  2. All data from: Engels 1978, p. 157
  3. Heckel, Waldemar: Who's Who in the Age of Alexander the Great: Prosopography of Alexander's Empire, Blackwell, 2006, ISBN 978-1-4051-1210-9, p. 26
  4. Heckel, Waldemar: Who's Who in the Age of Alexander the Great: Prosopography of Alexander's Empire, Blackwell, 2006, ISBN 978-1-4051-1210-9, p. 216
  5. Epigraphical Database: Elis — Olympia — 336–323 BC

Sources
  • Engels, Donald W.: Alexander the Great and the Logistics of the Macedonian Army, University of California Press, Los Angeles 1978, ISBN 0-520-04272-7
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