Tabellarius nuntiat reginam cras ad urbem venturam esse.

Because this sentence uses an indirect statement after nuntiat.

In Latin, after verbs like say, report, think, know, and announce, the person or thing being talked about often goes into the accusative, and the verb of that reported statement goes into an infinitive.

So:

• Tabellarius nuntiat = The messenger announces
• reginam ... venturam esse = that the queen will come

Here, reginam is the subject of the indirect statement, so it is accusative.

Venturam esse is the verb phrase of the indirect statement, and it means will come or is going to come.

It is made of:

• venturam = the future active participle of venio
• esse = to be

Together, venturam esse literally means something like to be about to come, but in normal English we usually translate it as will come.

So:

• reginam venturam esse = that the queen will come

Because venturam has to agree with reginam.

The participle venturus, ventura, venturum behaves like an adjective, so it must match the noun it describes in:

• gender
• number
• case

Since reginam is:

• feminine
• singular
• accusative

the participle must also be:

• feminine
• singular
• accusative

So we get venturam.

If the subject were masculine, you would get venturum or venturos depending on number and case.

This is a very common question.

The future meaning does not come from esse by itself. It comes from the combination:

• future participle
  • esse

So venturam esse is the normal Latin way to express future time in an indirect statement.

The infinitive esse stays infinitive because it is part of the indirect statement construction. The future idea is already built into venturam.

A useful comparison:

• venire = to come
• venisse = to have come
• venturam esse = to be going to come / to come later / will come

Because Latin usually does not use a separate word like English that in this kind of sentence.

English says:

• The messenger announces that the queen will come tomorrow

Latin usually prefers:

• The messenger announces the queen to be about to come tomorrow

That literal English sounds unnatural, but it shows the Latin structure more clearly.

So instead of a that-clause, Latin often uses:

• accusative + infinitive

That is exactly what we have here with reginam ... venturam esse.

Cras means tomorrow, and it modifies the action of coming.

So it belongs with venturam esse, not really with nuntiat.

The sense is:

• The messenger announces [today / now] that the queen will come tomorrow

It does not mean that the announcing happens tomorrow. It means the coming happens tomorrow.

Because ad shows motion toward a place.

• ad urbem = to the city

Latin often uses ad + accusative for movement toward something.

So:

• venire ad urbem = to come to the city

Without ad, the meaning would be different or much less straightforward here.

Urbem is accusative singular.

It is accusative because it is the object of the preposition ad, and ad takes the accusative case.

So:

• ad
  • accusative
• urbem = accusative singular of urbs

A useful way to divide it is:

• Tabellarius = subject
• nuntiat = main verb
• reginam cras ad urbem venturam esse = indirect statement

Inside the indirect statement:

• reginam = subject of the indirect statement
• cras = tomorrow
• ad urbem = to the city
• venturam esse = will come

So the whole structure is:

• [Main clause] The messenger announces
• [Indirect statement] that the queen will come to the city tomorrow

Yes, Latin word order is fairly flexible.

This sentence could be rearranged in several ways without changing the basic grammar, because the endings show the relationships:

• Tabellarius nuntiat reginam cras ad urbem venturam esse
• Reginam tabellarius cras ad urbem venturam esse nuntiat
• Cras reginam ad urbem venturam esse tabellarius nuntiat

However, word order still affects emphasis.

In the given sentence, the order is quite natural:

• main clause first
• then the reported statement

Also, putting venturam esse at the end is very typical Latin style, since verbs often come late.

In this exact sentence, with nuntiat in the present, the natural meaning is:

• The messenger announces that the queen will come tomorrow

The future infinitive expresses action later than the main verb.

So the timeline is:

• first: the messenger announces
• later: the queen comes

If the main verb were past, the English would often shift too:

• Tabellarius nuntiavit reginam cras ad urbem venturam esse
• The messenger announced that the queen would come to the city the next day / tomorrow

So venturam esse means future relative to the main verb, not necessarily future from the speaker’s present moment.

Tabellarius means a messenger, courier, or sometimes a letter-carrier.

It comes from tabellae, meaning letters or documents/tablets.

So the person is someone who carries messages or letters. Depending on context, English might translate it as:

• messenger
• courier
• letter-carrier
• postman (in some contexts)

In this sentence, messenger is a good general translation.

Here are the likely dictionary forms:

• tabellarius → tabellarius, -i = messenger
• nuntiat → nuntio, nuntiare, nuntiavi, nuntiatum = announce, report
• reginam → regina, -ae = queen
• cras = tomorrow
• ad = to, toward
• urbem → urbs, urbis = city
• venturam → from venio, venire, veni, ventum = come
• esse → from sum, esse, fui = be

A learner often finds venturam hard to identify, because it comes from the supine stem vent-, not from the present stem veni-.

So seeing venturam, you should think:

• vent- → from venio
• future participle → venturus, ventura, venturum