Roman odometer. Artwork of a type of odometer (for measuring distances travelled) described by 1st-century BC Roman engineer Vitruvius. It may have been originally been invented by Archimedes of Syracuse, with a similar device described by Hero of Alexandria. As the device moved forward on its wheels, a drive belt and system of cogs turn a central cogwheel. This would turn once per Roman mile (about 1400 metres) and drop a pebble (top) into a box (lower left). The pebbles were counted to determine the distance travelled.