Numerals
Latin numbers come in four flavors. Cardinals (ūnus, duo, trēs, quattuor) count how many; ordinals (prīmus, secundus, tertius) rank what position; distributives (singulī, bīnī, ternī) say how many each; numeral adverbs (semel, bis, ter) say how many times.
The good news: most cardinals from quattuor through centum don't decline at all — you just memorize the word.
The trap is the few that DO decline: ūnus, duo, trēs, the hundreds (ducentī, trecentī…), and mīlle — and mīlle itself flips between an indeclinable adjective in the singular and a noun (mīlia) in the plural that demands a partitive genitive.
Roman numerals work the same way English does, with one quirk: 18 and 19 are usually duodēvīgintī and ūndēvīgintī — "two from twenty," "one from twenty."
How many · which in order · how many each · how many times — every Latin number lives in one of these four columns.
Of the cardinals, only ūnus, duo, trēs, the hundreds, and mīlle decline. quattuor through centum are frozen forms — no endings to learn.
| Case | M. | F. | N. |
|---|---|---|---|
| Nom. | ūn-us | ūn-a | ūn-um |
| Gen. | ūn-īus | ūn-īus | ūn-īus |
| Dat. | ūn-ī | ūn-ī | ūn-ī |
| Acc. | ūn-um | ūn-am | ūn-um |
| Abl. | ūn-ō | ūn-ā | ūn-ō |
| Case | M. | F. | N. |
|---|---|---|---|
| Nom. | duo | duae | duo |
| Gen. | duōrum | duārum | duōrum |
| Dat. | duōbus | duābus | duōbus |
| Acc. | duōs (duo) | duās | duo |
| Abl. | duōbus | duābus | duōbus |
| Case | M./F. | N. |
|---|---|---|
| Nom. | trēs | tria |
| Gen. | trium | trium |
| Dat. | tribus | tribus |
| Acc. | trēs (trīs) | tria |
| Abl. | tribus | tribus |
See It In Action
— B. G. i.1.1
The opening line of the Gallic War packs three numeral types into one sentence: cardinal trēs (acc. f. pl.), the pronominal ūnam, and the ordinal tertiam. Notice tertiam declines like a normal 1st/2nd adjective.
— B. G. i.22.4
Roman miles literally counted paces: mīlia passuum tria = "three thousands of paces." mīlia is the noun (neuter pl.), passuum is the partitive genitive that comes with it.
— B. G. i.10.3
Watch the contrast: duās and trēs both decline (here in the accusative), but quīnque sits frozen — the case sense rides entirely on legiōnibus. That's the rule for 4-100.
— B. G. v.23.6
Two ordinals doing real work: secunda vigilia (the second night-watch — Romans split the night into four) and prīmā lūce ("at the first light" = dawn). Ordinals carry time of day and time of night in Caesar.
"N + noun" — straight count
quīnque legiōnibus = "with five legions"
"at the Nth + time-word" — prīmā lūce, secundā vigiliā
prīmā lūce = "at first light" (= at dawn)
"N thousand of X" — flip the counted noun to genitive
duo mīlia hominum = "two thousand men"
"N + plural-only noun" — read as a simple count, NOT "N each"
bīna castra = "two camps" (not "camps two each")
"two/one from twenty" → translate as 18 / 19
ūndēvīgintī mīlitēs = "19 soldiers"
"N times M" — multiplies the number that follows
bis bīna = "twice two" (= four)
mīlle in the singular is an indeclinable adjective; mīlia in the plural is a noun that takes a genitive.
modifies a noun directly
mīlle mīlitēs
a thousand soldiers
takes a partitive genitive
duo mīlia mīlitum
two thousand (of) soldiers
Tip: Ask: is the number 1000, or 2000+? At 1000 it's an adjective (nom. matches); at 2000+ it's a noun and the counted thing flips to genitive.
Caesar writes milia passuum tria ab eorum castris castra ponit (B. G. i.22.4). Why is passuum in the genitive?
Study Tips
- •Drill 1-10 first as a chant, then tens to 100, then 200, 500, 1000. That's your full counting vocabulary in about 35 words.
- •Practice the duo / trēs / mīlle paradigms until they're automatic — those are the only declensions you'll actually meet in Caesar.
- •When you see mīlia in the wild, look for the genitive that follows: mīlia passuum (miles), mīlia hominum (men). That noun-with-genitive pattern is your tip-off.