Ancient Roman units of measurement#Volume
{{Short description|System of measurement used in Ancient Rome}}{{Use dmy dates|date=July 2020}}
File:Modio de Ponte Puñide (M.A.N. 1930-16-1) 01.jpg
The units of measurement of ancient Rome were generally consistent and well documented.
Length
File:Roman milestone St Margarethen Austria 201 aC.jpg.]]
The basic unit of Roman linear measurement was the pes (plural: pedes) 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
| class="wikitable" style="margin: 1em auto 1em auto"
|+ Values of the ancient Roman foot determined by Greaves in 1639 |
| Source
! Reported value ! Metric |
|---|
| Foot on the statue of Cossutius
|align="center" |0.967 |align="right" | {{cvt|0.967|ft|mm|disp=out}} |
| Foot on the monument of Statilius
|align="center" |0.972 |align="right" | {{cvt|0.972|ft|mm|disp=out}} |
| Foot of Villalpandus, derived from Congius of Vespasian
|align="center" |0.986 |align="right" | {{cvt|0.986|ft|mm|disp=out}} |
William Smith (1851) gives a value of 0.9708 English feet, or about 295.9 mm. An accepted modern value is 296 mm. That foot is also called the pes monetalis to distinguish it from the pes Drusianus (about 333 or 335 mm) sometimes used in some provinces, particularly Germania Inferior.
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:
| class="wikitable" style="margin: 1em auto 1em auto"
|+Ancient Roman units of length |
| Roman unit
! English ! Equal ! Metric ! Imperial ! Notes |
|---|
| digitus
| finger |align="right" | {{frac|1|16}} pes |align="right" |18.5 mm |align="right" |0.728 in | |
| uncia pollex | inch |align="right" | {{frac|1|12}} pes |align="right" |24.6 mm |align="right" | 0.971 in | |
| palmus (minor)
| palm |align="right" | {{frac|1|4}} pes |align="right" |74 mm |align="right" |0.243 ft | |
| palmus maior
| palm length ({{abbr|lit.|literally}}"greater palm") |align="right" | {{frac|3|4}} pes |align="right" |222 mm |align="right" |0.728 ft | in late times |
| pes (plural: pedes)
|align="right" | 1 pes |align="right" |296 mm |align="right" |0.971 ft |sometimes distinguished as the pes monetalis{{efn|The pes Drusianus, 333 or 335 mm, was sometimes used in Roman provinces, particularly Germania Inferior.{{Cite book |last=Dilke |first=Oswald Ashton Wentworth |title=Mathematics and measurement |date=1987 |publisher=British Museum Publications |isbn=978-0-7141-8067-0 |series=Reading the past |location=London|pages=26–27}}{{Cite journal |last=Duncan-Jones |first=R. P. |date=1980 |title=Length-Units in Roman Town Planning: The Pes Monetalis and the Pes Drusianus |url=https://www.jstor.org/stable/525675 |journal=Britannia |volume=11 |pages=127–133 |doi=10.2307/525675|jstor=525675 }}}} |
| palmipes
| foot and a palm |align="right" | {{frac|1|1|4}} pedes |align="right" |370 mm |align="right" |1.214 ft | |
| cubitum
| cubit |align="right" | {{frac|1|1|2}} pedes |align="right" |444 mm |align="right" |1.456 ft | |
| gradus pes sestertius | step |align="right" | {{frac|2|1|2}} pedes |align="right" |0.74 m |align="right" |2.427 ft | |
| passus
| pace |align="right" | 5 pedes |align="right" |1.48 m |align="right" |4.854 ft | |
| decempeda pertica | perch |align="right" | 10 pedes |align="right" |2.96 m |align="right" |9.708 ft | |
| {{vanchor|Actus|text=actus}}
|path, track |align="right" | 120 pedes |align="right" |35.5 m |align="right" |116.496 ft |
| stadium
| stade |align="right" | 625 pedes |align="right" |185 m |align="right" |607.14 ft | 600 Greek feet |
| mille passus mille passuum |align="right" | 5,000 pedes |align="right" |1.48 km |align="right" |4,854 ft | 1000 passus or 8 stadia |
| leuga leuca | (Gallic) league |align="right" | 7,500 pedes |align="right" |2.22 km |align="right" |7,281 ft | |
| colspan=6 style= "font-size:smaller" | Except where noted, based on Smith (1851). 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 {{convert|5|km|mile|0|abbr=in|disp=or}}){{cite book|url=https://books.google.com/books?id=DQgmOZlsEWcC|title=Between Rome and Persia: The Middle Euphrates, Mesopotamia and Palmyra Under Roman Control|first=Peter|last=Edwell|year=2007|publisher=Routledge|page=228|isbn=9781134095735}}{{cite book|url=https://books.google.com/books?id=41-0AwAAQBAJ&pg=PT105|title=Amurath to Amurath: Includes Biography of Gertrude Bell|first1=Gertrude|last1=Bell|author-link1=Gertrude Bell|first2=Fergus|last2=Mason|year=2014|publisher=BookCaps Study Guides|page=105|isbn=9781629172859}} and in the name of the Nubian land of Triacontaschoenus between the First and Second Cataracts on the Nile (where it had a value closer to {{convert|10.5|km|mile|frac=2|abbr=in|disp=or}}).{{cite book|url=https://books.google.com/books?id=Or5CKl1ObX4C|title=The Histories|last=Herodotus|year=1998|publisher=OUP Oxford|page=592|isbn=9780191589553}}{{cite book|url=https://books.google.com/books?id=jjBYQCpfCNkC|title=The Cambridge History of Africa|first=J. D.|last=Fage|year=1979|publisher=Cambridge University Press|page=258|isbn=9780521215923}}
Area
The ordinary units of measurement of area were:
| class="wikitable" style="margin: 1em auto 1em auto"
|+ Ancient Roman units of area |
| Roman unit
! English ! Equal ! Metric ! Imperial ! Description |
|---|
| pes quadratus
| square foot |align="right" | 1 pes qu. |align="right" | 0.0876 m{{sup|2}} |align="right" | 0.943 sq ft | |
| style="max-width:0" | scrupulum or decempeda quadrata
| |align="right" | 100 pedes qu. |align="right" | 8.76 m{{sup|2}} |align="right" | 94.3 sq ft | style="max-width:0" | the square of the standard 10-foot measuring rod |
| actus simplex
| |align="right" | 480 pedes qu. |align="right" | 42.1 m{{sup|2}} |align="right" | 453 sq ft |
| uncia
| |align="right" | 2,400 pedes qu. |align="right" | 210 m{{sup|2}} |align="right" | 2,260 sq ft | |
| clima
| |align="right" | 3,600 pedes qu. |align="right" | 315 m{{sup|2}} |align="right" | 3,390 sq ft |
| actus quadratus or acnua
| |align="right" | 14,400 pedes qu. |align="right" | 1,262 m{{sup|2}} |align="right" | 13,600 sq ft |also called arpennis in Gaul |
| jugerum
| |align="right" | 28,800 pedes qu. |align="right" | 2,523 m{{sup|2}} |align="right" | 27,200 sq ft | |
| heredium
| |align="right" | 2 jugera |align="right" | 5,047 m{{sup|2}} |align="right" | 54,300 sq ft | |
| centuria
| |align="right" | 200 jugera |align="right" | 50.5 ha |align="right" | 125 acres |
| saltus
| |align="right" | 800 jugera |align="right" | 201.9 ha |align="right" | 499 acres | |
| modius
| |align="right" | |align="right" | 16 ha |align="right" | 40 acres |Medieval Latin, plural modii{{cite book|last=Davies |first=Wendy|authorlink=Wendy Davies |title=An Early Welsh Microcosm: Studies in the Llandaff Charters|page=33|publisher=Royal Historical Society |location =London, UK |year=1978|isbn=978-0-901050-33-5}} |
| colspan=6 style= "font-size:smaller" | Except where noted, based on Smith (1851). 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 {{convert|473|m2|sqft|abbr=on|disp=or}}) used in Hispania Baetica and the Gallic candetum or cadetum of 100 feet{{clarify|reason=100 square feet or 100 feet square (i.e. 10,000 square feet)?|date=October 2016}} 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:
| class="wikitable" style="margin: 1em auto 1em auto"
|+Uncial divisions of the jugerum |
| Roman unit ! Roman ! Fraction ! Metric ! Imperial ! Description |
|---|
| dimidium scrupulum
|align="right" | 50 |align="right" | {{frac|1|576}} |align="right" | 4.38 m{{sup|2}} |align="right" | 47.1 sq ft | |
| scrupulum
|align="right" | 100 |align="right" | {{frac|1|288}} |align="right" | 8.76 m{{sup|2}} |align="right" | 94.3 sq ft | |
| duo scrupula
|align="right" | 200 |align="right" | {{frac|1|144}} |align="right" | 17.5 m{{sup|2}} |align="right" | 188 sq ft | |
| sextula
|align="right" | 400 |align="right" | {{frac|1|72}} |align="right" | 35.0 m{{sup|2}} |align="right" | 377 sq ft | |
| sicilicus
|align="right" | 600 |align="right" | {{frac|1|48}} |align="right" | 52.6 m{{sup|2}} |align="right" | 566 sq ft | |
| semiuncia
|align="right" | 1,200 |align="right" | {{frac|1|24}} |align="right" | 105 m{{sup|2}} |align="right" | 1,130 sq ft | |
| uncia
|align="right" | 2,400 |align="right" | {{frac|1|12}} |align="right" | 210 m{{sup|2}} |align="right" | 2,260 sq ft | |
| sextans
|align="right" | 4,800 |align="right" | {{frac|1|6}} |align="right" | 421 m{{sup|2}} |align="right" | 4,530 sq ft | |
| quadrans
|align="right" | 7,200 |align="right" | {{frac|1|4}} |align="right" | 631 m{{sup|2}} |align="right" | 6,790 sq ft | |
| triens
|align="right" | 9,600 |align="right" | {{frac|1|3}} |align="right" | 841 m{{sup|2}} |align="right" | 9,050 sq ft | |
| quincunx
|align="right" | 12,000 |align="right" | {{frac|5|12}} |align="right" | 1,051 m{{sup|2}} |align="right" | 11,310 sq ft | |
| semis
|align="right" | 14,400 |align="right" | {{frac|1|2}} |align="right" | 1,262 m{{sup|2}} |align="right" | 15,380 sq ft |
| septunx
|align="right" | 16,800 |align="right" | {{frac|7|12}} |align="right" | 1,472 m{{sup|2}} |align="right" | 15,840 sq ft | |
| bes
|align="right" | 19,200 |align="right" | {{frac|2|3}} |align="right" | 1,682 m{{sup|2}} |align="right" | 18,100 sq ft | |
| dodrans
|align="right" | 21,600 |align="right" | {{frac|3|4}} |align="right" | 1,893 m{{sup|2}} |align="right" | 20,380 sq ft | |
| dextans
|align="right" | 24,000 |align="right" | {{frac|5|6}} |align="right" | 2,103 m{{sup|2}} |align="right" | 22,640 sq ft | |
| deunx
|align="right" | 26,400 |align="right" | {{frac|11|12}} |align="right" | 2,313 m{{sup|2}} |align="right" | 24,900 sq ft | |
| jugerum
|align="right" | 28,800 |align="right" | 1 |align="right" | 2,523 m{{sup|2}} |align="right" | 27,160 sq ft | |
| colspan=6 style= "font-size:smaller" | Except where noted, based on Millar (1745). Metric equivalents are approximate, converted at 1 pes = 296 mm. |
Volume
Both liquid and dry volume measurements were based on the {{lang|la|sextarius}}. The sextarius was defined as {{frac|48}} of a cubic {{lang|la|pes}} (Roman foot), known as an {{lang|la|amphora quadrantal}}. Using the value {{convert|296|mm|in|abbr=on}} for the Roman foot, an amphora quadrantal can be computed at approximately {{convert|25.9|L|abbr=on}}, so a sextarius (by the same method) would theoretically measure {{convert|540.3|ml|floz|abbr=on}}, which is about 95% of an imperial pint ({{cvt|1.000|imppt|ml|disp=out}}).
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 {{convert|500|and(-)|580|ml|USfloz|abbr=on}}.{{cite web|url=http://www.masseiana.org/pliny.htm|title=Pliny's Natural History (Introduction to Chapter 6)|author=W.H. Jones|year=1954|access-date=1 June 2014|archive-url=https://web.archive.org/web/20170101063545/http://www.masseiana.org/pliny.htm|archive-date=1 January 2017|url-status=usurped}}
The core volume units are:
- amphora quadrantal (Roman jar) – one cubic pes (Roman foot)
- congius – a half-pes cube (thus {{frac|1|8}} amphora quadrantal)
- sextarius – literally {{frac|1|6}} of a congius
=Liquid measure=
=Dry measure=
| class="wikitable"
|+ Ancient Roman dry measures |
| Roman unit
! Equal to ! Metric ! Imperial ! US dry |
|---|
| style="padding:0 8px;"| ligula
|style="padding:0 8px; text-align:right;"| {{frac|1|288}} congius |style="padding:0 8px; text-align:right;"| 11.4 ml |style="padding:0 8px; text-align:right;"| 0.401 fl oz |style="padding:0 8px; text-align:right;"| 0.0207 pt |
| style="padding:0 8px;"| cyathus
|style="padding:0 8px; text-align:right;"| {{frac|1|72}} congius |style="padding:0 8px; text-align:right;"| 45 ml |style="padding:0 8px; text-align:right;"| 1.58 fl oz |style="padding:0 8px; text-align:right;"| 0.082 pt |
| style="padding:0 8px;"| acetabulum
|style="padding:0 8px; text-align:right;"| {{frac|1|48}} congius |style="padding:0 8px; text-align:right;"| 68 ml |style="padding:0 8px; text-align:right;"| 2.39 fl oz |style="padding:0 8px; text-align:right;"| 0.124 pt |
| style="padding:0 8px;"| quartarius
|style="padding:0 8px; text-align:right;"| {{frac|1|24}} congius |style="padding:0 8px; text-align:right;"| 136 ml |style="padding:0 8px; text-align:right;"| 4.79 fl oz |style="padding:0 8px; text-align:right;"| 0.247 pt |
| style="padding:0 8px;"| hemina or cotyla
|style="padding:0 8px; text-align:right;"| {{frac|1|12}} congius |style="padding:0 8px; text-align:right;"| 273 ml |style="padding:0 8px; text-align:right;"| 9.61 fl oz |style="padding:0 8px; text-align:right;"| 0.496 pt |
| style="padding:0 8px;"| sextarius
|style="padding:0 8px; text-align:right;"| {{frac|1|6}} congius |style="padding:0 8px; text-align:right;"| 546 ml |style="padding:0 8px; text-align:right;"| 19.22 fl oz |style="padding:0 8px; text-align:right;"| 0.991 pt |
| style="padding:0 8px;"| semimodius
|style="padding:0 8px; text-align:right;"| {{frac|1|1|3}} congii |style="padding:0 8px; text-align:right;"| 4.36 L |style="padding:0 8px; text-align:right;"| 0.96 gal |style="padding:0 8px; text-align:right;"| 0.99 gal |
| style="padding:0 8px;"| modius
|style="padding:0 8px; text-align:right;"| {{frac|2|2|3}} congii |style="padding:0 8px; text-align:right;"| 8.73 L |style="padding:0 8px; text-align:right;"| 1.92 gal |style="padding:0 8px; text-align:right;"| 1.98 gal |
| style="padding:0 8px;"| modius castrensis
|style="padding:0 8px; text-align:right;"| 4 congii |style="padding:0 8px; text-align:right;"| 12.93 LDominic 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. |style="padding:0 8px; text-align:right;"| 2.84 gal |style="padding:0 8px; text-align:right;"| 2.94 gal |
| colspan=5 style="font-size:smaller;"| Except where noted, based on Smith (1851). Modern equivalents are approximate. |
Weight
File:Roman steelyard weight (probably) (FindID 227547).jpg
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 {{convert|322|to|329|g|oz|abbr=on}} with 5076 grains or {{convert|328.9|g|oz|abbr=on}} an accepted figure. 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 131 BC Lex Papiria.{{Citation |title=Oxford English Dictionary |edition=1st |contribution=as, n. |date=1885 |publisher=Oxford University Press |location=Oxford}}.{{Citation |title=A Dictionary of Greek and Roman Antiquities|contribution=Tabellariae Leges. |date=1875 |publisher=John Murray |location=London}}.
The divisions of the libra were:
| class="wikitable" style="margin: 1em auto 1em auto"
|+Uncial divisions of the libra |
| Roman unit
! English ! Equal ! Metric ! Imperial ! Description |
|---|
| uncia
| Roman ounce |align="right" | {{frac|1|12}} libra |align="right" | 27.4 g |align="right" | 0.967 oz |{{abbr|lit.|literally}} "a twelfth"{{Cite web |title=Charlton T. Lewis, Charles Short, A Latin Dictionary, U , umbrōsus , uncĭa |url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0059:alphabetic+letter=U:entry+group=3:entry=uncia |access-date=2024-08-08 |website=www.perseus.tufts.edu}} |
| sescuncia or sescunx
| |align="right" | {{frac|1|8}} libra |align="right" | 41.1 g |align="right" | 1.45 oz |{{abbr|lit.|literally}} "one and one-half twelfths" |
| sextans
| |align="right" | {{frac|1|6}} libra |align="right" | 54.8 g |align="right" | 1.93 oz |{{abbr|lit.|literally}} "a sixth" |
| quadrans teruncius | |align="right" | {{frac|1|4}} libra |align="right" | 82.2 g |align="right" | 2.90 oz |{{abbr|lit.|literally}} "a fourth" |
| triens
| |align="right" | {{frac|1|3}} libra |align="right" | 109.6 g |align="right" | 3.87 oz |{{abbr|lit.|literally}} "a third" |
| quincunx
| |align="right" | {{frac|5|12}} libra |align="right" | 137.0 g |align="right" | 4.83 oz |{{abbr|lit.|literally}} "five-twelfths"{{Citation |title=Oxford English Dictionary, 3rd ed. |contribution=quincunx, n. |date=2007 |publisher=Oxford University Press |location=Oxford}}. |
| semis or semissis
| |align="right" | {{frac|1|2}} libra |align="right" | 164.5 g |align="right" | 5.80 oz |{{abbr|lit.|literally}} "a half" |
| septunx
| |align="right" | {{frac|7|12}} libra |align="right" | 191.9 g |align="right" | 6.77 oz |{{abbr|lit.|literally}} "seven-twelfths" |
| bes or bessis
| |align="right" | {{frac|2|3}} libra |align="right" | 219.3 g |align="right" | 7.74 oz |{{abbr|lit.|literally}} "two [parts] of an as" |
| dodrans
| |align="right" | {{frac|3|4}} libra |align="right" | 246.7 g |align="right" | 8.70 oz |{{abbr|lit.|literally}} "less a fourth" |
| dextans
| |align="right" | {{frac|5|6}} libra |align="right" | 274.1 g |align="right" | 9.67 oz |{{abbr|lit.|literally}} "less a sixth" |
| deunx
| |align="right" | {{frac|11|12}} libra |align="right" | 301.5 g |align="right" | 10.64 oz |{{abbr|lit.|literally}} "less a twelfth" |
| libra
|align="right" | |align="right" | 328.9 g |align="right" | 11.60 oz | {{abbr|lit.|literally}} "balance"{{Citation |title=Oxford English Dictionary, 1st ed. |contribution=libra, n. |date=1902 |publisher=Oxford University Press |location=Oxford}}. |
| colspan=6 style= "font-size:smaller" | Except where noted, based on Smith (1851). Metric equivalents are approximate, converted at 1 libra = 328.9 g . |
The subdivisions of the uncia were:
| class="wikitable" style="margin: 1em auto 1em auto"
|+Subdivisions of the uncia |
| Roman unit
! English ! Equal ! Metric ! Imperial ! Description |
|---|
| siliqua
| carat |align="right" | {{frac|1|144}} uncia |align="right" | 0.19 g |align="right" | 2.9 gr | {{abbr|lit.|literally}} "carob seed" |
| obolus
|align="right" | {{frac|1|48}} uncia |align="right" | 0.57 g |align="right" | 8.8 gr | {{abbr|lit.|literally}} "obol", from the Greek word for "metal spit" |
| scrupulum
| scruple |align="right" | {{frac|1|24}} uncia |align="right" | 1.14 g |align="right" | 17.6 gr | {{abbr|lit.|literally}} "small pebble"{{Citation |title=Oxford English Dictionary, 1st ed. |contribution=scruple, n.1 |date=1911 |publisher=Oxford University Press |location=Oxford}}. |
| semisextula or dimidia sextula
| |align="right" | {{frac|1|12}} uncia |align="right" | 2.28 g |align="right" | 35.2 gr | {{abbr|lit.|literally}} "half-sixth", "little sixth" |
| sextula
|align="right" | {{frac|1|6}} uncia |align="right" | 4.57 g |align="right" | 70.5 gr | {{abbr|lit.|literally}} "little sixth"{{Citation |title=Oxford English Dictionary, 3rd ed. |contribution=sextula, n. |date=2008 |publisher=Oxford University Press |location=Oxford}}. |
| sicilicus or siciliquus
| |align="right" | {{frac|1|4}} uncia |align="right" | 6.85 g |align="right" | 106 gr |{{abbr|lit.|literally}} "little sickle" |
| duella
| |align="right" | {{frac|1|3}} uncia |align="right" | 9.14 g |align="right" | 141 gr | {{abbr|lit.|literally}} "little double [sixths]" |
| semuncia
|align="right" | {{frac|1|2}} uncia |align="right" | 13.7 g |align="right" | 211 gr | {{abbr|lit.|literally}} "half-twelfth"{{Citation |title=Oxford English Dictionary, 1st ed. |contribution=semuncia, n. |date=1911 |publisher=Oxford University Press |location=Oxford}}. |
| uncia
| Roman ounce |align="right" | |align="right" | 27.4 g |align="right" | 423 gr |
| colspan=6 style= "font-size:smaller" | Except where noted, based on Smith (1851). Metric equivalents are approximate, converted at 1 libra = 328.9 g . |
Time
{{unreferenced section|date=November 2011}}
=Years=
The complicated Roman calendar was replaced by the Julian calendar in 45 BC.{{cite web|url=https://www.timeanddate.com/calendar/julian-calendar.html|title=The Julian Calendar|website=timeanddate.com|access-date=2019-05-25}} In the Julian calendar, an ordinary year is 365 days long, and a leap 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 the Roman 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 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, based on the supposed birth year of Jesus.
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 (i.e. 97 leap years in every 400) to more closely approximate the length of the tropical year.
=Weeks=
The Romans grouped days into an eight-day cycle called the {{lang|la|nundinae}}, with every eighth day being a market day.
Independent of the {{lang|la|nundinae}}, astrologers kept a seven-day cycle called a hebdomas 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, Jupiter-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 begins at sunset. Christians followed the Jewish seven-day week, except that they commonly called the first day of the week the {{lang|la|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=
{{main article|Roman timekeeping}}
The Romans divided the daytime into twelve horae or hours 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 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, Classical astrologers had a minuta equal to {{frac|60}} of a day (24 modern minutes), a secunda equal to {{frac|3600}} of a day (24 modern seconds), and a tertia equal to {{frac|216,000}} of a day (0.4 modern seconds).
Unicode
{{special characters|unicode}}
{{Main article|Ancient Symbols (Unicode block)}}
{{see also|Unicode input}}
A number of special symbols for Roman currency were added to the Unicode Standard version 5.1 (April 2008) as the Ancient Symbols block (U+10190–U+101CF, in the Supplementary Multilingual Plane ).
{{Unicode chart Ancient Symbols}}
As mentioned above, the names for divisions of an {{lang|la|as}} 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:
- U+10190 (𐆐): Sextans
- U+10191 (𐆑): Uncia
- U+10192 (𐆒): Semuncia
- U+10193 (𐆓): Sextula
- U+10194 (𐆔): Semisextula
- U+10195 (𐆕): Siliqua
See also
Notes
{{notelist}}