Roman units

The ancient Roman units of measurement were largely built on the Hellenic system, which in turn was built upon Egyptian and Mesopotamian influences. The Roman units were comparatively consistent and well documented.

The basic unit of Roman linear measurement was the pes or Roman foot. Investigation of its relation to the English foot goes back at least to 1647, when John Greaves published his Discourse on the Romane foot. Greaves visited Rome in 1639, and measured, among other things, the foot measure on the tomb of Titus Statilius Aper, that on the statue of Cossutius formerly in the gardens of Angelo Colocci, the congius of Vespasian previously measured by Villalpandus, a number of brass measuring-rods found in the ruins of Rome, the paving-stones of the Pantheon and many other ancient Roman buildings, and the distance between the milestones on the Appian Way. He concluded that the Cossutian foot was the "true" Roman foot, and reported these values compared to the iron standard of the English foot in the Guildhall in London (30.4919 cm):

Smith (1851) gives a value of 0.9708 English feet, or about 295.9 mm. An accepted modern value is 296 mm.

The Roman foot was sub-divided either like the Greek pous into 16 digiti or fingers; or into 12 unciae or inches. Frontinus writes in the 1st century AD that the digitus was used in Campania and most parts of Italy. The principal Roman units of length were:

Other units include the schoenus (from the Greek for "rush rope") used for the distances in Isidore of Charax's Parthian Stations (where it had a value around 5 km or 3 miles) and in the name of the Nubian land of Triakontaschoenus between the First and Second Cataracts on the Nile (where it had a value closer to 10.5 km or 6 ¹⁄₂ miles).

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