Postea quaestor cum praefecto portus de merce ex Sicilia allata loquitur.

Because loquitur comes from the deponent verb loquor, loqui, locutus sum, which has passive forms but active meanings.

So:

• loquitur = he/she speaks, not he/she is spoken
• It is 3rd person singular present

This is a very common feature in Latin, and loquor is one of the first important deponent verbs learners meet.

The subject is quaestor.

It is in the nominative singular, and it means the quaestor. Since loquitur is 3rd person singular, it matches quaestor as the subject:

• quaestor ... loquitur = the quaestor speaks / is speaking

Because the preposition cum meaning with takes the ablative case.

So:

• cum praefecto = with the prefect

Here praefecto is the ablative singular of praefectus.

This is one of the most basic and frequent Latin patterns:

• cum + ablative = with ...

Here portus means of the harbor/port and is a genitive singular.

So:

• praefecto portus = the prefect of the harbor

A learner might find this confusing because portus is a 4th-declension noun, and in the 4th declension the genitive singular often looks the same as the nominative singular.

So although portus can mean harbor as a dictionary form, here its role in the sentence shows that it is genitive:

• praefectus portus = prefect of the harbor

Because de takes the ablative case.

So:

• de merce = about the merchandise/goods

This is another standard Latin pattern:

• de + ablative = about, concerning, down from, from

In this sentence, the meaning is clearly about/concerning.

Because the noun is governed by de, which requires the ablative.

The dictionary form is:

• merx, mercis = merchandise, goods

Its ablative singular is:

• merce

So:

• de merce = about the merchandise

Even though English often uses a plural idea like goods, Latin can use the singular merx as a collective noun meaning merchandise or cargo.

Because allata agrees with merce.

Here allata is a participle, from affero (bring to, carry to), and it means brought. Since it describes merce, it must match it in:

• gender: feminine
• number: singular
• case: ablative

So:

• merce ... allata = the merchandise ... having been brought / brought

Because merce is ablative singular feminine, allata must also be ablative singular feminine.

It means brought from Sicily.

Breakdown:

• ex Sicilia = from Sicily
• allata = brought

Together they describe merce:

• de merce ex Sicilia allata = about the merchandise brought from Sicily

Also note that ex takes the ablative, so Sicilia appears as Sicilia in the ablative singular.

In sense, it goes most closely with allata:

• allata ex Sicilia = brought from Sicily

But the whole phrase ex Sicilia allata describes merce.

So grammatically you can think of it like this:

• merce = the noun
• allata = participle modifying the noun
• ex Sicilia = phrase completing the participle’s meaning

In natural English, we usually bundle it together:

• the merchandise brought from Sicily

Because Latin word order is much more flexible than English word order, and it is very common for the verb to come at or near the end.

So this sentence is arranged in a very Latin way:

• Postea = time word first
• quaestor = subject
• cum praefecto portus = with whom he is speaking
• de merce ex Sicilia allata = what he is speaking about
• loquitur = verb at the end

A more word-for-word English order would sound unnatural, but Latin often likes to save the verb until the end.

Postea is an adverb meaning afterwards, later, or then.

It tells you when the action happens:

• Postea ... loquitur = Afterwards / Later ... he speaks

Latin often places time words like this near the beginning of the sentence to set the scene right away.

Yes. Cum can also be a conjunction meaning when, since, or although. But here it is definitely the preposition with.

You can tell because:

• it is followed by praefecto, an ablative noun
• the sense is clearly with the prefect

So here:

• cum praefecto = with the prefect

not

• when the prefect...

Yes. A fairly literal version would be:

• Afterwards the quaestor speaks with the prefect of the harbor about the merchandise brought from Sicily.

A very close structural rendering would be:

• Afterwards the quaestor with the prefect of the harbor about the merchandise brought from Sicily speaks.

That second version is not good English, but it helps show how the Latin sentence is built.