Bematists or bematistae (Ancient Greek βηματισταί (bēmatistaí, ‘step measurer’), from βῆμα (bema, ‘pace’)), were specialists in ancient Greece and ancient Egypt who were trained to measure distances by counting their steps, i.e., pacing.

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 accuracy 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

Wikipedia: Bematist