Ancient Roman units of measurement

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Bronze modius measure (4th century AD) with inscription acknowledging Imperial regulation of weights and measures

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

Length[edit]

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:[1]

Values of the ancient Roman foot determined by Greaves in 1639
Source Reported value in English feet Metric equivalent
Foot on the statue of Cossutius 0.967  294.7 mm 
Foot on the monument of Statilius 0.972  296.3 mm 
Foot of Villalpandus, derived from Congius of Vespasian 0.986  300.5 mm 
Metric equivalents are approximate.

Smith (1851) gives a value of 0.9708 English feet, or about 295.9 mm.[2] An accepted modern value is 296 mm.[3]

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.[4] The principal Roman units of length were:

Ancient Roman units of length
Roman unit English name Equal to English equivalent Metric equivalent Notes
digitus finger 116 pes 0.728 in 
0.0607 ft 
18.5 mm 
uncia
pollex
inch
thumb
112 pes 0.971 in 
0.0809 ft 
24.6 mm 
palmus palm width 14 pes 0.243 ft  74 mm 
palmus major palm length 34 pes 0.728 ft  222 mm  in late times
pes (Roman) foot 1 pes 0.971 ft  296 mm 
palmipes 114 pedes 1.214 ft  370 mm 
cubitus cubit 112 pedes 1.456 ft  444 mm 
gradus
pes sestertius
step 212 pedes 2.427 ft  0.74 m 
passus pace 5 pedes 4.854 ft  1.48 m 
decempeda
pertica
perch 10 pedes 9.708 ft  2.96 m 
actus (length) 120 pedes 116.496 ft  35.5 m 
stadium stade 625 pedes 607.14 ft  185 m  600 Greek feet
Equivalent to the English furlong
mille passus
mille passuum
(Roman) mile 5000 pedes 4854 ft 
0.919 mi 
1.48 km 
leuga (Gallic) league 7500 pedes 7281 ft 
1.379 mi 
2.22 km 
Except where noted, based on Smith (1851).[2] English and Metric equivalents are approximate, converted at 1 pes = 0.9708 English feet and 296 mm respectively.

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)[5][6] 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).[7][8]

Area[edit]

The ordinary units of measurement of area were:

Ancient Roman units of area
Roman unit English name Equal to Metric equivalent Description
pes quadratus square foot 1 pes² 0.0876 m² 
scrupulum or decempeda quadrata 100 pedes² 8.76 m²  the square of the standard 10-foot measuring rod
actus simplex 480 pedes² 42.1 m²  4 × 120 pedes[9]
uncia 2400 pedes² 210 m² 
clima 3600 pedes² 315 m²  60 × 60 pedes[9]
actus quadratus or acnua 14400 pedes² 1262 m²  also called arpennis in Gaul[9]
jugerum 28800 pedes² 2523 m² 
heredium 2 jugera 5047 m² 
centuria 200 jugera 50.5 ha  formerly 100 jugera[9]
saltus 800 jugera 201.9 ha 
Except where noted, based on Smith (1851).[2] Metric equivalents are approximate, converted at 1 pes = 296 mm.

Other units of area described by Columella in his De Re Rustica include the porca of 180 × 30 Roman feet (about 473 m²) used in Hispania Baetica and the Gallic candetum or cadetum of 100 feet in the city or 150 in the country. Columella also gives uncial divisions of the jugerum, tabulated by the anonymous translator of the 1745 Millar edition as follows:

Uncial divisions of the jugerum
Roman unit Roman square feet Fraction of jugerum Metric equivalent Description
dimidium scrupulum 50 1576 4.38 m² 
scrupulum 100 1288 8.76 m² 
duo scrupula 200 1144 17.5 m² 
sextula 400 172 35.0 m² 
sicilicus 600 148 52.6 m² 
semiuncia 1200 124 105 m² 
uncia 2400 112 210 m² 
sextans 4800 16 421 m² 
quadrans 7200 14 631 m² 
triens 9600 13 841 m² 
quincunx 12000 512 1051 m² 
semis 14400 12 1262 m²  = actus quadratus[2]
septunx 16800 712 1472 m² 
bes 19200 23 1682 m² 
dodrans 21600 34 1893 m² 
dextans 24000 56 2103 m² 
deunx 26400 1112 2313 m² 
jugerum 28800 1 2523 m² 
Except where noted, based on Millar (1745).[9] Metric equivalents are approximate, converted at 1 pes = 296 mm.

Volume[edit]

Both liquid and dry measures were based on the sextarius. As no two surviving examples are identical, scholarly opinion ranges from 0.53 l[10] to 0.58 l.[11] Cardarelli gives a value 0.54928 l.[12] A 1952 estimate for its value in Pliny the Elder's Natural History estimated it as 500 ml.[13]

Since the Romans themselves defined the sextarius as 1/48th of an amphora quadrantal, and the amphora quadrantal as one cubic foot, assuming a value of 296 mm for the Roman foot yields a theoretical value for the sextarius of about 540.3 ml, which falls comfortably within the accepted range.

The core volume units are:

  • amphora quadrantal (Roman jar) – one cubic pes (Roman foot)
  • congius – a half-pes cube (thus 18 amphora quadrantal)
  • sextarius – literally 16, of a congius

Liquid measures[edit]

Ancient Roman liquid measures
Roman unit Equal to Metric
ligula 1288 congius 11.4 ml
cyathus 172 congius 45 ml
acetabulum 148 congius 68 ml
quartarius 124 congius 136 ml
hemina or cotyla 112 congius 273 ml
sextarius 16 congius 546 ml
congius 1 congius 3.27 l
urna 4 congii 13.1 l
amphora quadrantal 8 congii 26.2 l
culeus 160 congii 524 l
Except where noted, based on Smith (1851).[2]
Metric equivalents are approximate.

Dry measures[edit]

Ancient Roman dry measures
Roman unit Equal to Metric
ligula 1288 congius 11.4 ml
cyathus 172 congius 45 ml
acetabulum 148 congius 68 ml
quartarius 124 congius 136 ml
hemina or cotyla 112 congius 273 ml
sextarius 16 congius 546 ml
semimodius 1 13 congii 4.36 l
modius 2 23 congii 8.73 l (or 8.62 l)
modius castrensis 4 congii (12.93 l?)[14]
Except where noted, based on Smith (1851).[2]
Metric equivalents are approximate.

Weight[edit]

The units of weight or mass were mostly based on factors of 12. Several of the unit names were also the names of coins during the Roman Republic and had the same fractional value of a larger base unit: libra for weight and as for coin. Modern estimates of the libra range from 322 to 329 grams (11.4 to 11.6 oz) with 5076 grains or 328.9 grams (11.60 oz) an accepted figure.[3][11][15] The as was reduced from 12 ounces to 2 after the First Punic War, to 1 during the Second Punic War, and to half an ounce by the 191 BC Lex Papiria.[16]

The divisions of the libra were:

Uncial divisions of the libra
Roman unit English name Equal to Metric equivalent Description
uncia Roman ounce 112 libra 27.4 g  lit. "a twelfth"[17]
sescuncia or sescunx 18 libra 41.1 g  lit. "1½-twelfths"
sextans 16 libra 54.8 g  lit. "a sixth"
quadrans
teruncius
14 libra 82.2 g  lit. "a fourth"
lit. "triple twelfth"
triens 13 libra 109.6 g  lit. "a third"
quincunx 512 libra 137.0 g  lit. "five-twelfths"[18]
semis or semissis 12 libra 164.5 g  lit. "a half"
septunx 712 libra 191.9 g  lit. "seven-twelfths"
bes or bessis 23 libra 219.3 g  lit. "two [parts] of an as"
dodrans 34 libra 246.7 g  lit. "less a fourth"
dextans 56 libra 274.1 g  lit. "less a sixth"
deunx 1112 libra 301.5 g  lit. "less a twelfth"
libra Roman pound
libra[19]
328.9 g  lit. "balance"[19]
Except where noted, based on Smith (1851).[2] Metric equivalents are approximate, converted at 1 libra = 328.9 g .

The subdivisions of the uncia were:

Subdivisions of the uncia
Roman unit English name Equal to Metric equivalent Description
siliqua carat 1144 uncia 0.19 g  lit. "carob seed"
The Greek κεράτιον (kerátion)
obolus obolus[20] 148 uncia 0.57 g  lit. "obol", from the Greek word for "metal spit"[20]
scrupulum scruple[21] 124 uncia 1.14 g  lit. "small pebble"[21]
semisextula 112 uncia 2.28 g  lit. "half-little sixth"
sextula sextula[22] 16 uncia 4.57 g  lit. "little sixth"[22]
sicilicus
siciliquus
14 uncia 6.85 g  lit. "little sickle"
duella 13 uncia 9.14 g  lit. "little double [sixths]"
semuncia half-ounce
semuncia[23]
12 uncia 13.7 g  lit. "half-twelfth"[23]
uncia Roman ounce 27.4 g 
Except where noted, based on Smith (1851).[2] Metric equivalents are approximate, converted at 1 libra = 328.9 g .

Time[edit]

Years[edit]

The complicated Roman calendar was replaced by the Julian calendar in 45 BC. In the Julian calendar, an ordinary year is 365 days long, and a leap year is 366 days long. Between 45 BC and 1 AD, leap years occurred at irregular intervals. Starting in the year 4 AD, leap years occurred regularly every four years. Year numbers were rarely used; rather, the year was specified by naming the Roman consuls for that year. When a year number was required, the Greek Olympiads were used, or the count of years since the founding of Rome, "ab urbe condita" in 753 BC. In the middle ages, the year numbering was changed to the Anno Domini count.

The calendar used in most of the modern world, the Gregorian calendar, differs from the Julian calendar in that it skips three leap years every four centuries to more closely approximate the length of the tropical year.

Weeks[edit]

The Romans grouped days into an eight-day cycle called a nundina, with every eighth day being a market day.

Independent of the nundinae, astrologers kept a seven-day cycle called a hebdomada where each day corresponded to one of the seven classical planets, with the first day of the week being Saturn-day, followed by Sun-day, Moon-day, Mars-day, Mercury-day, Jove-day, and lastly Venus-day. Each astrological day was reckoned to begin at sunrise. The Jews also used a seven-day week, which began Saturday evening. The seventh day of the week they called Sabbath; the other days they numbered rather than named, except for Friday, which could be called either the Parasceve or the sixth day. Each Jewish day was reckoned to begin at sunset. Christians followed the Jewish seven-day week, except that they commonly called the first day of the week the Dominica, or the Lord's day. In 321 Constantine the Great gave his subjects every Sunday off in honor of his family's tutelary deity, the Unconquered Sun, thus cementing the seven-day week into Roman civil society.

Hours[edit]

Main article: Roman timekeeping

The Romans divided the daytime into twelve horae or hours starting in the morning and ending in the evening. The night was divided into four watches. The duration of these hours varied with seasons; in the winter, when the daylight period was shorter, its 12 hours were correspondingly shorter and its four watches were correspondingly longer.

Astrologers divided the solar day into 24 equal hours, and these astrological hours became the basis for medieval clocks and our modern 24-hour mean solar day.

Although the division of hours into minutes and seconds did not occur until the middle ages, ancient astrologers had a minuta equal to a 60th of a day (24 modern minutes), and a secunda equal to one 3600th of a day (24 modern seconds).

Unicode[edit]

Ancient Roman units of measurement were added to the Unicode Standard in April, 2008 with the release of version 5.1.

The Unicode block for ancient Roman units of measurement, called Ancient Symbols, is U+10190–U+101CF, i.e. in the upper plane:

Ancient Symbols[1][2]
Official Unicode Consortium code chart (PDF)
  0 1 2 3 4 5 6 7 8 9 A B C D E F
U+1019x 𐆐 𐆑 𐆒 𐆓 𐆔 𐆕 𐆖 𐆗 𐆘 𐆙 𐆚 𐆛
U+101Ax 𐆠
U+101Bx
U+101Cx
Notes
1.^ As of Unicode version 7.0
2.^ Grey areas indicate non-assigned code points

See also[edit]

References[edit]

  1. ^ Greaves, John (1647) A discourse of the Romane foot and denarius; from whence, as from two principles, the measures and weights used by the ancients may be deduced London: William Lee
  2. ^ a b c d e f g h Smith, Sir William; Charles Anthon (1851) A new classical dictionary of Greek and Roman biography, mythology, and geography partly based upon the Dictionary of Greek and Roman biography and mythology New York: Harper & Bros. Tables, pp. 1024–30
  3. ^ a b Hosch, William L. (ed.) (2010) The Britannica Guide to Numbers and Measurement New York, NY: Britannica Educational Publications, 1st edition. ISBN 978-1-61530-108-9, p.206
  4. ^ Sextus Julius Frontinus (c. 100 AD) De aquis 1:24. English translation.
  5. ^ 3.
  6. ^ 4.
  7. ^ 5.
  8. ^ 6.
  9. ^ a b c d e Lucius Junius Moderatus Columella, Anon. (trans.) (1745) L. Junius Moderatus Columella of Husbandry, in Twelve Books: and his book, concerning Trees. Translated into English, with illustrations from Pliny, Cato, Varro, Palladius and other ancient and modern authors London: A. Millar. pp xiv, 600. Pages 208–216.
  10. ^ Inc NetLibrary, inc Encyclopædia Britannica (2009). Encyclopædia Britannica almanac 2008. Encyclopædia Britannica. p. 162. ISBN 978-1-59339-475-2. Retrieved December 2011. 
  11. ^ a b Zupko, Ronald Edward (1977). British weights & measures: a history from antiquity to the seventeenth century. University of Wisconsin Press. p. 7. Retrieved 9 December 2011. 
  12. ^ Cardarelli, François; M.J. Shields (tr.) (2003). Encyclopaedia of Scientific Units, Weights and Measures: Their SI Equivalences and Origins. Springer. pp. 74–5. ISBN 9781852336820. 
  13. ^ W.H. Jones (1954). "Pliny's Natural History (Introduction to Chapter 6)". 
  14. ^ Dominic Rathbone, "Earnings and Costs: Living Standards and the Roman Economy (First to Third Centuries AD), p. 301, in Alan Bowman and Andrew Wilson, Quantifying the Roman Economy: Methods and Problems.
  15. ^ Skinner, Frederick George (1967). Weights and measures: their ancient origins and their development in Great Britain up to A.D. 1855. H.M.S.O. p. 65. Retrieved 9 December 2011. 
  16. ^ "as, n.", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1885 .
  17. ^ "ounce, n.1", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911 .
  18. ^ "quincunx, n.", Oxford English Dictionary, 3rd ed., Oxford: Oxford University Press, 2007 .
  19. ^ a b "libra, n.", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1902 .
  20. ^ a b "obelus, n.", Oxford English Dictionary, 3rd ed., Oxford: Oxford University Press, 2004 .
  21. ^ a b "scruple, n.1", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911 .
  22. ^ a b "sextula, n.", Oxford English Dictionary, 3rd ed., Oxford: Oxford University Press, 2008 .
  23. ^ a b "semuncia, n.", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911 .

External links[edit]