Master Latin cardinal and ordinal numbers, Roman numerals, telling time the Roman way, and the Roman calendar system — including the Kalends, Nones, and Ides that gave us our month names.
Estimated Time: 40–50 minutes
The first three numbers decline (change by gender and case). Four through ten do not.
| # | Latin | Notes |
|---|---|---|
| 1 | ūnus, ūna, ūnum | Declines like a 1st/2nd decl. adjective |
| 2 | duo, duae, duo | Irregular declension |
| 3 | trēs, tria | 3rd declension (m/f: trēs, n: tria) |
| 4 | quattuor | Indeclinable (doesn't change) |
| 5 | quīnque | Indeclinable |
| 6 | sex | Indeclinable |
| 7 | septem | Indeclinable |
| 8 | octō | Indeclinable |
| 9 | novem | Indeclinable |
| 10 | decem | Indeclinable |
| 11 | ūndecim | ūnus + decem |
| 12 | duodecim | duo + decem |
| 13 | trēdecim | |
| 14 | quattuordecim | |
| 15 | quīndecim | |
| 16 | sēdecim | |
| 17 | septendecim | |
| 18 | duodēvīgintī | "two from twenty" |
| 19 | ūndēvīgintī | "one from twenty" |
| 20 | vīgintī |
Latin counts 18 as "two from twenty" and 19 as "one from twenty." This subtractive pattern repeats: 28 = duodētrīgintā ("two from thirty"), 29 = ūndētrīgintā ("one from thirty"), and so on.
| # | Latin | # | Latin |
|---|---|---|---|
| 30 | trīgintā | 100 | centum |
| 40 | quadrāgintā | 200 | ducentī, -ae, -a |
| 50 | quīnquāgintā | 500 | quīngentī |
| 60 | sexāgintā | 1,000 | mīlle |
| 70 | septuāgintā | 2,000 | duo mīlia |
| 80 | octōgintā | 10,000 | decem mīlia |
| 90 | nōnāgintā | 100,000 | centum mīlia |
Mīlle (1,000) is an indeclinable adjective: mīlle mīlitēs = "a thousand soldiers." But the plural mīlia is a neuter noun that takes the genitive: duo mīlia mīlitum = "two thousands of soldiers."
Ordinals decline like regular 1st/2nd declension adjectives (-us, -a, -um):
| # | Ordinal | # | Ordinal |
|---|---|---|---|
| 1st | prīmus, -a, -um | 7th | septimus |
| 2nd | secundus / alter | 8th | octāvus |
| 3rd | tertius | 9th | nōnus |
| 4th | quārtus | 10th | decimus |
| 5th | quīntus | 20th | vīcēsimus |
| 6th | sextus | 100th | centēsimus |
You already know these — now see them as Latin abbreviations:
| Symbol | Value | Origin |
|---|---|---|
| I | 1 | One finger |
| V | 5 | Open hand (five fingers) |
| X | 10 | Two hands crossed |
| L | 50 | Half of the old symbol for 100 |
| C | 100 | From centum |
| D | 500 | Half of the old symbol for 1000 |
| M | 1000 | From mīlle |
Subtractive rule: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900. A smaller symbol before a larger one means subtraction.
The Roman calendar didn't number days 1–30. Instead, it counted backward from three fixed reference points in each month:
| Reference Point | Name | Date (most months) | Date (Mar, May, Jul, Oct) |
|---|---|---|---|
| 1st of the month | Kalendae (Kalends) | 1st | 1st |
| Early middle | Nōnae (Nones) | 5th | 7th |
| Middle | Īdūs (Ides) | 13th | 15th |
The Ides of March (March 15th) is famous as the date Julius Caesar was assassinated in 44 BC. The soothsayer's warning — Cave Īdūs Mārtiās! — is one of history's most famous phrases. Shakespeare made it immortal in English.
Romans counted inclusively backward from the next reference point. So March 13th wasn't "March 13" — it was "the third day before the Ides of March" (ante diem tertium Īdūs Mārtiās, abbreviated a.d. III Īd. Mārt.).
| Latin | English | Origin |
|---|---|---|
| Iānuārius | January | Janus, god of doorways and beginnings |
| Februārius | February | Februa, purification festival |
| Mārtius | March | Mars, god of war (original first month) |
| Aprīlis | April | Possibly Aphrodite, or aperīre (to open) |
| Māius | May | Maia, goddess of growth |
| Iūnius | June | Juno, queen of the gods |
| Iūlius | July | Julius Caesar (renamed from Quīntīlis) |
| Augustus | August | Emperor Augustus (renamed from Sextīlis) |
| September | September | Septem — 7th month (in the old calendar) |
| Octōber | October | Octō — 8th month |
| November | November | Novem — 9th month |
| December | December | Decem — 10th month |
The original Roman calendar started in March (the beginning of the military campaign season). September through December were genuinely the 7th–10th months. When January and February were added to the beginning, the names stuck even though the numbering shifted.
Romans divided daylight into 12 hōrae (hours) and nighttime into 4 vigiliae (watches). Hours varied in length with the seasons — a summer hour was longer than a winter hour.
| Latin | Approximate Modern Time |
|---|---|
| hōra prīma (first hour) | ~6:00 AM (sunrise) |
| hōra tertia (third hour) | ~9:00 AM |
| hōra sexta (sixth hour) | ~12:00 noon |
| hōra nōna (ninth hour) | ~3:00 PM |
| hōra duodecima (twelfth hour) | ~6:00 PM (sunset) |
The monastic prayer hours (Lauds, Prime, Terce, Sext, None, Vespers, Compline) preserve this Roman time system. None (the ninth hour, ~3 PM) is the origin of the English word "noon" — it shifted earlier over the centuries as monks moved their midday meal.
Match the Latin number to its English word descendant:
1. How did Romans express the number 18?
2. Why is September named "seventh" when it's the 9th month?
3. What are the Ides of March (Īdūs Mārtiāe)?
✦ Numbers 1–3 decline; 4–10 are indeclinable. 18/19 use subtraction: "two/one from twenty."
✦ Mīlle (1000) is an adjective; mīlia (thousands) is a noun taking the genitive.
✦ Roman calendar counted backward from Kalends (1st), Nones (5th/7th), and Ides (13th/15th).
✦ Month names September–December reflect the old calendar starting in March.
✦ Roman hours varied in length — 12 hours of daylight, 4 night watches.