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Theunits of measurement ofancient Rome were generally consistent and well documented.
The basic unit of Roman linear measurement was thepes (plural:pedes) orRoman foot. Investigation of its relation to theEnglish foot goes back at least to 1647, whenJohn Greaves published hisDiscourse 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 ofAngelo Colocci, thecongius ofVespasian previously measured byVillalpandus, a number of brass measuring-rods found in the ruins of Rome, the paving-stones of thePantheon and many other ancient Roman buildings, and the distance between the milestones on theAppian 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 theGuildhall in London[1]
| Source | Reported value in English feet | Metric equivalent |
|---|---|---|
| Foot on the statue of Cossutius | 0.967 | 295 mm |
| Foot on the monument of Statilius | 0.972 | 296 mm |
| Foot ofVillalpandus, derived fromCongius of Vespasian | 0.986 | 301 mm |
William Smith (1851) gives a value of 0.9708 English feet, or about 295.9 mm.[2] An accepted modern value is 296 mm.[3] That foot is also called thepes monetalis to distinguish it from thepes Drusianus (about 333 or 335 mm) sometimes used in some provinces, particularlyGermania Inferior.[4][5]
The Roman foot was sub-divided either like the Greekpous into 16digiti or fingers; or into 12unciae or inches.Frontinus writes in the 1st century AD that thedigitus was used inCampania and most parts of Italy.[6] The principal Roman units of length were:
| Roman unit | English name | Equal to | Metric equivalent | Imperial equivalent | Notes |
|---|---|---|---|---|---|
| digitus | finger | 1⁄16 pes | 18.5 mm | 0.728 in 0.0607 ft | |
| uncia pollex | inch thumb | 1⁄12 pes | 24.6 mm | 0.971 in 0.0809 ft | |
| palmus (minor) | palm | 1⁄4 pes | 74 mm | 0.243 ft | |
| palmus maior | palm length (lit."greater palm") | 3⁄4 pes | 222 mm | 0.728 ft | in late times |
| pes (plural: pedes) | (Roman)foot | 1 pes | 296 mm | 0.971 ft | sometimes distinguished as thepes monetalis[a] |
| palmipes | foot and a palm | 1+1⁄4 pedes | 370 mm | 1.214 ft | |
| cubitum | cubit | 1+1⁄2 pedes | 444 mm | 1.456 ft | |
| gradus pes sestertius | step | 2+1⁄2 pedes | 0.74 m | 2.427 ft | |
| passus | pace | 5 pedes | 1.48 m | 4.854 ft | |
| decempeda pertica | perch | 10 pedes | 2.96 m | 9.708 ft | |
| actus | path, track | 120 pedes | 35.5 m | 116.496 ft | 24 passus or12 decembeda |
| stadium | stade | 625 pedes | 185 m | 607.14 ft | 600Greek feet or 125 passus or1⁄8 mille[7] |
| mille passus mille passuum | (Roman)mile | 5,000 pedes | 1.48 km | 4,854 ft 0.919 mi | 1000 passus or 8 stadia |
| leuga leuca | (Gallic)league | 7,500 pedes | 2.22 km | 7,281 ft 1.379 mi | |
| 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 theschoenus (from the Greek for "rush rope") used for the distances inIsidore of Charax'sParthian Stations (where it had a value around 5 km or 3 miles)[8][9] and in the name of theNubian land ofTriacontaschoenus between theFirst andSecond Cataracts on theNile (where it had a value closer to10.5 km or6+1⁄2 miles).[10][11]
The ordinary units of measurement of area were:
| Roman unit | English name | Equal to | Metric equivalent | Imperial equivalent | Description |
|---|---|---|---|---|---|
| pes quadratus | square foot | 1 pes qu. | 0.0876 m2 | 0.943 sq ft | |
| scrupulum or decempeda quadrata | 100 pedes qu. | 8.76 m2 | 94.3 sq ft | the square of the standard 10-foot measuring rod | |
| actus simplex | 480 pedes qu. | 42.1 m2 | 453 sq ft | 4 × 120 pedes[12] | |
| uncia | 2,400 pedes qu. | 210 m2 | 2,260 sq ft | ||
| clima | 3,600 pedes qu. | 315 m2 | 3,390 sq ft | 60 × 60 pedes[12] | |
| actus quadratus or acnua | 14,400 pedes qu. | 1,262 m2 | 13,600 sq ft | also calledarpennis inGaul[12] | |
| jugerum | 28,800 pedes qu. | 2,523 m2 | 27,200 sq ft 0.623 acres | ||
| heredium | 2 jugera | 5,047 m2 | 54,300 sq ft 1.248 acres | ||
| centuria | 200 jugera | 50.5ha | 125 acres | formerly 100 jugera[12] | |
| saltus | 800 jugera | 201.9 ha | 499 acres | ||
| modius | 16 ha | 40 acres | Medieval Latin, plural modii[13] | ||
| Except where noted, based on Smith (1851).[2] Metric equivalents are approximate, converted at 1 pes = 296 mm. | |||||
Other units of area described byColumella in hisDe Re Rustica include theporca of 180 × 30 Roman feet (about 473 m2 or 5,090 sq ft) used inHispania Baetica and the Galliccandetum orcadetum of 100 feet[clarification needed] in the city or 150 in the country. Columella also gives uncial divisions of thejugerum, tabulated by the anonymous translator of the 1745 Millar edition as follows:
| Roman unit | Roman square feet | Fraction of jugerum | Metric equivalent | Imperial equivalent | Description |
|---|---|---|---|---|---|
| dimidium scrupulum | 50 | 1⁄576 | 4.38 m2 | 47.1 sq ft | |
| scrupulum | 100 | 1⁄288 | 8.76 m2 | 94.3 sq ft | |
| duo scrupula | 200 | 1⁄144 | 17.5 m2 | 188 sq ft | |
| sextula | 400 | 1⁄72 | 35.0 m2 | 377 sq ft | |
| sicilicus | 600 | 1⁄48 | 52.6 m2 | 566 sq ft | |
| semiuncia | 1,200 | 1⁄24 | 105 m2 | 1,130 sq ft | |
| uncia | 2,400 | 1⁄12 | 210 m2 | 2,260 sq ft | |
| sextans | 4,800 | 1⁄6 | 421 m2 | 4,530 sq ft | |
| quadrans | 7,200 | 1⁄4 | 631 m2 | 6,790 sq ft | |
| triens | 9,600 | 1⁄3 | 841 m2 | 9,050 sq ft | |
| quincunx | 12,000 | 5⁄12 | 1,051 m2 | 11,310 sq ft | |
| semis | 14,400 | 1⁄2 | 1,262 m2 | 15,380 sq ft | = actus quadratus[2] |
| septunx | 16,800 | 7⁄12 | 1,472 m2 | 15,840 sq ft | |
| bes | 19,200 | 2⁄3 | 1,682 m2 | 18,100 sq ft | |
| dodrans | 21,600 | 3⁄4 | 1,893 m2 | 20,380 sq ft | |
| dextans | 24,000 | 5⁄6 | 2,103 m2 | 22,640 sq ft | |
| deunx | 26,400 | 11⁄12 | 2,313 m2 | 24,900 sq ft | |
| jugerum | 28,800 | 1 | 2,523 m2 | 27,160 sq ft | |
| Except where noted, based on Millar (1745).[12] Metric equivalents are approximate, converted at 1 pes = 296 mm. | |||||
Both liquid and dry volume measurements were based on thesextarius. The sextarius was defined as1⁄48 of a cubicpes (Roman foot), known as anamphora quadrantal. Using the value 296 mm (11.7 in) for the Roman foot, an amphora quadrantal can be computed at approximately 25.9 L (5.7 imp gal; 6.8 US gal), so a sextarius (by the same method) would theoretically measure 540.3 ml (19.02 imp fl oz; 18.27 US fl oz), which is about 95% of animperial pint (568 ml).
Archaeologically, however, the evidence is not as precise. No two surviving vessels measure an identical volume, and scholarly opinion on the actual volume ranges between 500 and 580 ml (17–20 US fl oz).[14][15]
The core volume units are:
| Roman unit | Equal to | Metric | Imperial | US fluid |
|---|---|---|---|---|
| ligula | 1⁄288 congius | 11.4 mL | 0.401 fl oz | 0.385 fl oz |
| cyathus | 1⁄72 congius | 45 mL | 1.58 fl oz | 1.52 fl oz |
| acetabulum | 1⁄48 congius | 68 mL | 2.39 fl oz | 2.30 fl oz |
| quartarius | 1⁄24 congius | 136 mL | 4.79 fl oz | 4.61 fl oz |
| hemina or cotyla | 1⁄12 congius | 273 mL | 9.61 fl oz | 9.23 fl oz |
| sextarius | 1⁄6 congius | 546 mL | 19.22 fl oz 0.961 pt | 18.47 fl oz 1.153 pt |
| congius | 1 congius | 3.27 L | 5.75 pt 0.719 gal | 3.46 qt 0.864 gal |
| urna | 4 congii | 13.1 L | 2.88 gal | 3.46 gal |
| amphora quadrantal | 8 congii | 26.2 L | 5.76 gal | 6.92 gal |
| culeus | 160 congii | 524 L | 115.3 gal | 138.4 gal |
| Except where noted, based on Smith (1851).[2] Modern equivalents are approximate. | ||||
| Roman unit | Equal to | Metric | Imperial | US dry |
|---|---|---|---|---|
| ligula | 1⁄288 congius | 11.4 ml | 0.401 fl oz | 0.0207 pt |
| cyathus | 1⁄72 congius | 45 ml | 1.58 fl oz | 0.082 pt |
| acetabulum | 1⁄48 congius | 68 ml | 2.39 fl oz | 0.124 pt |
| quartarius | 1⁄24 congius | 136 ml | 4.79 fl oz | 0.247 pt |
| hemina or cotyla | 1⁄12 congius | 273 ml | 9.61 fl oz | 0.496 pt |
| sextarius | 1⁄6 congius | 546 ml | 19.22 fl oz 0.961 pt | 0.991 pt |
| semimodius | 1+1⁄3 congii | 4.36 L | 0.96 gal | 0.99 gal |
| modius | 2+2⁄3 congii | 8.73 L | 1.92 gal | 1.98 gal |
| modius castrensis | 4 congii | 12.93 L[16] | 2.84 gal | 2.94 gal |
| Except where noted, based on Smith (1851).[2] Modern equivalents are approximate. | ||||
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The units of weight ormass were mostly based on factors of 12. Several of the unit names were also the names of coins during theRoman Republic and had the same fractional value of a larger base unit: libra for weight andas for coin. Modern estimates of the libra range from 322 to 329 g (11.4 to 11.6 oz) with 5076 grains or 328.9 g (11.60 oz) an accepted figure.[3][15][17] Theas was reduced from 12 ounces to 2 after theFirst Punic War, to 1 during theSecond Punic War, and to half an ounce by the 131 BCLex Papiria.[18][19]
The divisions of the libra were:
| Roman unit | English name | Equal to | Metric equivalent | Imperial equivalent | Description |
|---|---|---|---|---|---|
| uncia | Roman ounce | 1⁄12 libra | 27.4 g | 0.967 oz | lit. "a twelfth"[20] |
| sescuncia or sescunx | 1⁄8 libra | 41.1 g | 1.45 oz | lit. "one and one-half twelfths" | |
| sextans | 1⁄6 libra | 54.8 g | 1.93 oz | lit. "a sixth" | |
| quadrans teruncius | 1⁄4 libra | 82.2 g | 2.90 oz | lit. "a fourth" lit. "triple twelfth" | |
| triens | 1⁄3 libra | 109.6 g | 3.87 oz | lit. "a third" | |
| quincunx | 5⁄12 libra | 137.0 g | 4.83 oz | lit. "five-twelfths"[21] | |
| semis or semissis | 1⁄2 libra | 164.5 g | 5.80 oz | lit. "a half" | |
| septunx | 7⁄12 libra | 191.9 g | 6.77 oz | lit. "seven-twelfths" | |
| bes or bessis | 2⁄3 libra | 219.3 g | 7.74 oz | lit. "two [parts] of anas" | |
| dodrans | 3⁄4 libra | 246.7 g | 8.70 oz | lit. "less a fourth" | |
| dextans | 5⁄6 libra | 274.1 g | 9.67 oz | lit. "less a sixth" | |
| deunx | 11⁄12 libra | 301.5 g | 10.64 oz | lit. "less a twelfth" | |
| libra | Roman pound libra[22] | 328.9 g | 11.60 oz 0.725 lb | lit. "balance"[22] | |
| 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:
| Roman unit | English name | Equal to | Metric equivalent | Imperial equivalent | Description |
|---|---|---|---|---|---|
| siliqua | carat | 1⁄144 uncia | 0.19 g | 2.9 gr 0.0067 oz | lit. "carob seed" The Greekκεράτιον (kerátion) |
| obolus | obolus[23] | 1⁄48 uncia | 0.57 g | 8.8 gr 0.020 oz | lit. "obol", from the Greek word for "metal spit"[23] |
| scrupulum | scruple[24] | 1⁄24 uncia | 1.14 g | 17.6 gr 0.040 oz | lit. "small pebble"[24] |
| semisextula or dimidia sextula | 1⁄12 uncia | 2.28 g | 35.2 gr 0.080 oz | lit. "half-sixth", "little sixth" | |
| sextula | sextula[25] | 1⁄6 uncia | 4.57 g | 70.5 gr 0.161 oz | lit. "little sixth"[25] |
| sicilicus or siciliquus | 1⁄4 uncia | 6.85 g | 106 gr 0.242 oz | lit. "littlesickle" | |
| duella | 1⁄3 uncia | 9.14 g | 141 gr 0.322 oz | lit. "little double [sixths]" | |
| semuncia | half-ounce semuncia[26] | 1⁄2 uncia | 13.7 g | 211 gr 0.483 oz | lit. "half-twelfth"[26] |
| uncia | Roman ounce | 27.4 g | 423 gr 0.967 oz | "a twelfth"[20] | |
| Except where noted, based on Smith (1851).[2] Metric equivalents are approximate, converted at 1 libra = 328.9 g . | |||||
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The complicatedRoman calendar was replaced by theJulian calendar in 45 BC.[27] In the Julian calendar, an ordinary year is 365 days long, and aleap year is 366 days long. Between 45 BC and AD 1, leap years occurred at irregular intervals. Starting in AD 4, leap years occurred regularly every four years. Year numbers were rarely used; rather, the year was specified by naming theRoman consuls for that year. (As consuls' terms latterly ran from January to December, this eventually caused January, rather than March, to be considered the start of the year.) When a year number was required, the GreekOlympiads were used, or the count of years since the founding of Rome, "ab urbe condita" in 753 BC. In theMiddle Ages, the year numbering was changed to theAnno Domini count, based on the supposed birth year ofJesus.
The calendar used in most of the modern world, theGregorian calendar, differs from the Julian calendar in that it skips three leap years every four centuries (i.e. 97 leap years in every 400) to more closely approximate the length of thetropical year.
The Romans grouped days into an eight-day cycle called thenundinae, with every eighth day being a market day.
Independent of thenundinae,astrologers kept a seven-day cycle called ahebdomas where each day corresponded to one of the sevenclassical planets, with the first day of the week beingSaturn-day, followed bySun-day,Moon-day,Mars-day,Mercury-day,Jupiter-day, and lastlyVenus-day. Each astrological day was reckoned to begin at sunrise. TheJews also used a seven-day week, which began Saturday evening. The seventh day of the week they calledSabbath; 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 begins at sunset.Christians followed the Jewish seven-day week, except that they commonly called the first day of the week theDominica, or theLord's day. In 321,Constantine the Great gave his subjects every Sunday off in honor of his family'stutelary deity, theUnconquered Sun, thus cementing the seven-day week into Roman civil society.
The Romans divided the daytime into twelvehorae orhours starting at sunrise and ending at sunset. 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 thesolar day into 24 equal hours, and these astrological hours became the basis for medievalclocks and our modern 24-hourmean solar day.
Although the division of hours intominutes andseconds did not occur until the Middle Ages,Classical astrologers had aminuta equal to1⁄60 of a day (24 modern minutes), asecunda equal to1⁄3600 of a day (24 modern seconds), and atertia equal to1⁄216,000 of a day (0.4 modern seconds).
A number of special symbols for Roman currency were added to theUnicode Standard version 5.1 (April 2008) as the Ancient Symbols block (U+10190–U+101CF, in the Supplementary Multilingual 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 | ||||||||||||||||
As mentioned above, the names for divisions of anas coin (originally one libra of bronze) were also used for divisions of a libra, and the symbols U+10190–U+10195 are likewise also symbols for weights: