- one Roman mile: 1480 m (1000 paces, or 2000 steps, or 5000 feet)
- one ride: 740 m (4 stadia, 1000 steps)
- one Roman stadium: 185 m (1/8 Roman mile, 250 steps, 625 feet), note this value is also equal to 1/10 nautical mile (or 1/10 of a minute of latitude); it is still in use today as a “cable”. This unit was used by Pliny and by Strabo.
- one Delphi stadium: 177.7 m (used by Strabo and by Polybius)
- one Olympia stadium: 192.3 m (also used by Strabo)
- one Egyptian stadium: 157.7 m (used by Eratosthenes and by Arrian)
Hence, before the Romans put some order into it, there was much confusion in the length of an ancient stadium! It was nevertheless much used by ancient seafarers, but they were more interested in the duration of trips than in accurate distances (see below).
- one Greek pleather: 30.8 m (100 feet, 40 steps), but also an area of 950 m2 (10 200 sq feet)
- one Greek fathom, orguia, orgye: 1,85 m (6 feet, 4 cubits)
- one Greek cubit: 0,462 m (24 fingers, 1.5 feet),
but one Egyptian cubit is 0,525 m
- one Greek foot: 0,308 m (16 fingers)
- one Greek finger: 19.25 mm
Other important units are:
- one Roman talent : (60 Roman minae, or 100 Roman libra) mass of ca. 33 kg. It is also an ancient currency: a Greek talent is 6000 Greek drachmas, or 24 000 Roman sesterces, but an Egyptian talent is only 6000 Roman sesterces.
- One sesterce: = 6.5 €, based on the fairly low annual salary of a 1st century soldier or worker of 1000 sesterces/year, compared to the French lowest revenue (RSA) of 6 420 €/year in 2016 for a single man.
- amphora quadrantal: as a volume, one amphora is one Roman cubic foot (nearly one modern cubic foot) = 2/3 artaba = 2 modii castrensis = 3 (Italic) modii = 8 congii = 48 sextarii, or 26 litres. A full amphora (olive oil, wine, fish brine) weights around 50 kg, out of which around half is tare (Dressel 1B amphora).
- It may be noted that Egyptian grain was transported in sacks of one artaba (39 litres) with a unit weight of 31.5 kg.
- Note also that wooden oak barrels (500 to 1000 litres) took over from amphorae (and dolia) for storage of wine during the Roman Empire.
- year of Rome (after Romulus’ calendar): starts at the foundation of Rome in 753 BC (and valid until 45 BC).
Among the distances, the “day of navigation” of a sailing cargo ship must be mentioned. In times without any charts, the measure of distance was focussed on the time required to sail a given distance more than on its correct value. This time of course depends on the wind and on the point of sailing. They nevertheless had a few benchmarks:
- 1 day of navigation (12 to 17 hours): 500 to 900 stadia (50 to 90 nautical miles) with an average of 700 stadia (70 nautical miles), that is 4 to 5 knots (4 to 5 nautical miles/hour) average speed.
- 1 day and 1 night (24 hours): around 1000 stadia (100 nautical miles), that is around 4 knots (4 nautical miles/hour) average speed.
For a trireme of the 5th century BC, an average speed of 5 knots is accepted for a duration of 10 to 15 hours/day. Under sail, these ships were a bit slower than under oar.
With a modern single hull tourism sailing boat, the values of the figures above are doubled.
A stable wind direction could be used as a guide and ancient wind roses were very detailed:
Wind directions are defined according to their origin: to sail eastward, you are pushed by a western wind (“westerlies”), typically like the Zephyr which leads to Alexandria (where they call it the “etesian winds” or “summer winds”) if you leave from … Zephyrion Acra (modern Capo Bruzzano, in Calabria).
“If a man does not know to which port he is steering, no wind is favorable to him” (Seneca, Epistolae, 71, 3).
 Eratosthenes (276-194 BC) already estimated the terrestrial meridian at 250 000 Egyptian stadia, that is 39 425 km. The circumference of the Earth being 360 x 60 = 21 600 minutes of latitude or as many nautical miles, one nautical mile therefore is 1823 m for Eratosthenes, which is remarkably close to today’s value of 1852 m. Eratosthenes also estimated the distance between Rhodes and Alexandria at 3 750 Egyptian stadia (acc. to Strabo, Geogr, 2, 5) that is 591 km, almost exactly what we would say today based on Google Earth (600 km from Mandraki to Pharos. It can be noted that Ptolemy (350 years later) will be heavily mistaken on these figures.
 Salary of one denarius = 4 sesterces = 16 asses per day, acc. to Tacitus, Annals, I, 17, and on 250 days/year, i.e. 1000 sesterces/year (around 110 AD).
Some time before Tacitus, Cato tells us in his De Agricultura, 22, 3 (around 160 BC) that « the charge for transportation by oxen, with six days’ wages of six men, drivers included, is 72 sesterces”, that is 2 sesterces/man-day or 5 asses/man-day (note that before 140 BC one denarius = 4 sesterces = 10 asses).
Inflation might be estimated as follows from the cost of one labourer’s man-day: ca. 0.5 denarius in 160 BC; 1 denarius in 110 AD; 4 denarii in 240 AD; 25 denarii in 301 AD in Diocletian Price Edict. The highest inflation rate (averaged from 240 to 301 AD) is around 3% per annum.
See also: https://web.archive.org/web/20130210071801/http://dougsmith.ancients.info/worth.html
 Ships were sailing from wind astern (180°) to wind abeam (90°), even if it was possible to sail into the wind up to around 60° (see Arnaud, 2005 and Morrison, 2000). Triremes could sail into the wind under oar, but could not accept more than 15-20 knots of wind ahead because of fatigue of the crew and too much waves (Morrison, 2000 et Rankov, 2012).
 A “long day” probably refers to a summer solstice day (Arnaud, 2014), that is 13.5 hours in Berenike Troglodytika, 14.0 hr in Alexandria, 15.0 hr in Istanbul, 15.6 hr in Aquileia, 16.0 hr in Paris.
 MORRISON, J.S.; COATES J.F.; RANKOV, N.B. « The Athenian Trireme », Cambridge University Press, 2000.
 ARNAUD, P. « Les routes de la navigation antique », éd. Errance, 2005.
The pictured wind rose is from Jules Vars in “L’art nautique dans l’antiquité et spécialement en Grèce”, Paris, 1887. It shows the archaic 2-direction wind rose (Boreas and Notos), the 4-direction rose, both 8-direction roses according to Homer and Aristotle, the 12-direction rose according to Timosthenes, the 24-direction rose by Vitruvius, and finally the 19th century 32-direction rose on the outer ring.