Ianitor portam urbis claudit, quia nox obscura est.

Ianitor is in the nominative singular, which is the case Latin normally uses for the subject of a verb.

So in Ianitor portam urbis claudit, ianitor is the person doing the action: the gatekeeper closes the gate.

A useful clue is the verb claudit, which is third-person singular: he/she/it closes. That matches a singular subject like ianitor.

Because portam is in the accusative singular. The accusative case is commonly used for the direct object, the thing directly affected by the action.

Here, the gatekeeper is closing the gate, so portam is the direct object.

• porta = gate
• portam = gate as the direct object

So:

• ianitor = subject
• portam = object

Urbis is the genitive singular of urbs, meaning of the city.

So portam urbis means the gate of the city or the city gate.

If you used urbs, that would be nominative, and it would not fit this phrase. Latin often uses the genitive to show possession or close relationship:

• porta urbis = gate of the city
• murus urbis = wall of the city

It is a noun phrase made of:

• portam = gate in the accusative
• urbis = of the city in the genitive

The main noun is portam, and urbis depends on it.

So the whole phrase means:

• the gate of the city
• or more naturally in English, the city gate

Even though English often puts the describing noun first, Latin commonly uses the genitive instead.

Claudit comes from claudere, meaning to close.

Its form is:

• present tense
• active voice
• indicative mood
• third-person singular

So it means he closes, she closes, or it closes.

In this sentence, since the subject is ianitor, it means the gatekeeper closes.

Latin word order is much more flexible than English word order because the endings show what each word is doing.

Putting the verb at the end is very common in Latin, especially in straightforward prose. So:

• Ianitor portam urbis claudit

is a very natural Latin order.

But Latin could also say, for example:

• Ianitor claudit portam urbis
• Portam urbis ianitor claudit

These all mean basically the same thing, though the emphasis may shift slightly.

Quia means because and introduces a clause giving the reason.

So the sentence is in two parts:

• Ianitor portam urbis claudit
• quia nox obscura est

The second part explains why the gatekeeper closes the gate: because the night is dark.

Because obscura is a predicate adjective, not a direct object.

In nox obscura est, both nox and obscura are in the nominative singular:

• nox = night
• obscura = dark
• est = is

So the structure is:

• night is dark

With forms of to be, Latin uses the nominative for both the subject and the predicate adjective.

Because it agrees with nox, which is a feminine noun.

Latin adjectives must agree with the nouns they describe in:

• gender
• number
• case

Since nox is:

• feminine
• singular
• nominative

the adjective must also be:

• feminine
• singular
• nominative

So we get obscura.

Yes, sometimes Latin can omit forms of esse (to be), especially in poetry or in more compressed style.

But in normal beginner-level prose, est is often stated clearly:

• nox obscura est = the night is dark

Leaving it in makes the sentence straightforward and easy to read. So this is the most expected form for a learner.

That is right: Classical Latin has no definite or indefinite article.

So Latin does not have separate words for:

• the
• a/an

Context tells you how to translate it.

For example:

• ianitor can mean a gatekeeper or the gatekeeper
• portam can mean a gate or the gate
• nox can mean night or the night

English has to choose, but Latin does not need to mark that distinction in the same way.

In a classical-style pronunciation, roughly:

• Ianitor = YA-ni-tor
• portam = POR-tam
• urbis = UR-bis
• claudit = KLOW-dit
• quia = KWI-a
• nox = noks
• obscura = ob-SKOO-ra
• est = est

A few useful pronunciation notes:

• initial I before a vowel in Ianitor sounds like English y
• c is always hard, so claudit begins with a k sound
• au in claudit sounds like the ow in cow
• qu is pronounced together, like kw

So the whole sentence is approximately:

YA-ni-tor POR-tam UR-bis KLOW-dit, KWI-a nox ob-SKOO-ra est.