Tribunus legatum audit et dicit rem publicam magno in periculo esse.

Because legatum is the direct object of audit.

• Tribunus = the tribune, so it is the subject
• audit = hears/listens to
• legatum = the envoy/legate, in the accusative singular

So Latin is showing: The tribune hears the envoy.

The noun is from legatus, legatī. Its accusative singular form is legatum.

Because it is the subject of an infinitive in an indirect statement.

After verbs like dicit (he says), Latin often uses this pattern:

• accusative subject
• infinitive verb

So instead of saying:

• rēs pūblica est in perīculō = the republic is in danger

Latin changes it after dicit to:

• dicit rem publicam esse in periculo = he says that the republic is in danger

That is why rēs pūblica becomes rem publicam.

Because after dicit, Latin uses an infinitive in indirect statement.

So:

• direct statement: rēs pūblica est in perīculō
• indirect statement: dicit rem publicam in periculo esse

In English, we often use that:

• He says that the republic is in danger

Latin usually does not use a word for that here. Instead, it uses accusative + infinitive:

• rem publicam esse

There is no separate word for it in this sentence.

English says:

• He says that the republic is in great danger

Latin usually expresses this by using indirect statement:

• dicit rem publicam magno in periculo esse

So the idea of that is built into the grammar, not shown by a separate word.

Because in periculo is a common expression meaning in danger, and periculo is ablative singular after in when the sense is location/state, not motion.

• in periculo = in danger
• magno agrees with periculo
• both are ablative singular masculine/neuter

So magno in periculo literally means in great danger.

Because Latin uses:

• in + ablative for being in something, or a state/location
• in + accusative for motion into something

Here the republic is already in danger, not moving into danger.

So:

• in periculo esse = to be in danger
• in periculum venire = to come into danger

That is why the sentence has in periculo, not in periculum.

Because rēs pūblica is a noun phrase made of a noun plus an adjective, and both words must match in case, number, and gender.

Base form:

• rēs pūblica = the republic / the state

In this sentence, the phrase is accusative singular because it is the subject of the infinitive in indirect statement:

• rem publicam

So:

• rēs → rem
• pūblica → pūblicam

Both change together.

It literally means the public thing, but in normal English it is usually translated as:

• the republic
• the state
• sometimes public affairs

In this sentence, the republic or the state is the most natural translation.

It can suggest either, depending on context.

From audiō, audīre, it often means:

• hear
• listen to
• listen

In this sentence, he hears the envoy is probably the most straightforward literal meaning, but if the context is a formal report or speech, he listens to the envoy may sound more natural in English.

Tribunus is nominative singular, because it is the subject of the two main verbs:

• audit
• dicit

So tribunus is the person doing both actions:

• The tribune hears...
• and says...

Because the same subject applies to both verbs.

Latin often states the subject once and then continues with more verbs joined by et:

• Tribunus legatum audit et dicit...

This means:

• The tribune hears the envoy and says...

You do not need to repeat tribunus before dicit.

It connects the two main verbs:

• audit
• dicit

So the basic structure is:

• Tribunus = subject
• audit = first action
• et = and
• dicit = second action

Then dicit introduces the indirect statement:

• rem publicam magno in periculo esse

Because Latin word order is much more flexible than English word order.

Placing esse at the end is very normal, especially in an indirect statement. Latin often saves the infinitive until the end:

• dicit rem publicam magno in periculo esse

This can help the sentence feel complete and balanced.

English usually wants:

• He says that the republic is in great danger

Latin is freer about where words go, as long as the endings make the grammar clear.

Yes. Latin word order is flexible, so many rearrangements are possible without changing the basic meaning, for example:

• Tribunus audit legatum et dicit rem publicam in magno periculo esse
• Legatum tribunus audit et dicit rem publicam magno in periculo esse

But the original order is perfectly normal. The endings tell you the grammatical roles, so Latin does not depend on word order as heavily as English does.

They are:

• tribunus, tribunī = tribune
• legatus, legatī = envoy, legate
• audiō, audīre, audīvī, audītum = hear, listen to
• dīcō, dīcere, dīxī, dictum = say
• rēs, reī = thing, affair
• pūblicus, pūblica, pūblicum = public
• magnus, magna, magnum = great, large
• perīculum, perīculī = danger
• sum, esse, fuī = be

It would be:

• Rēs pūblica magnō in perīculō est.
• The republic is in great danger.

When you put it after dicit, Latin changes it into indirect statement:

• dicit rem publicam magno in periculo esse
• he says that the republic is in great danger

That contrast is a very useful one to learn.