Quantus clamor hodie in foro est!

Here quantus is an exclamatory adjective. It means something like how great, how much, or what a ...! depending on how you translate it naturally in English.

So Quantus clamor! is not really asking for information. It is expressing surprise or emphasis: What a noise! or How great the shouting is!

Because quantus goes with a noun: here the noun is clamor.

• quantus clamor = what a great noise
• quam magnus clamor would mean something more like how great the noise is

A useful distinction:

• quantus modifies a noun
• quam often modifies an adjective or adverb

So in this sentence, since Latin is exclaiming about the amount/degree of noise itself, quantus is the natural choice.

Because it has to agree with clamor.

Clamor is:

• masculine
• singular
• nominative

So quantus is also:

• masculine
• singular
• nominative

This is normal adjective agreement in Latin: adjectives match the nouns they describe in gender, number, and case.

Clamor is nominative singular.

It is nominative because it is the subject of est:

• clamor est = the noise is / there is noise

Even though English might translate this more naturally as there is such a noise, Latin still treats clamor as the grammatical subject.

Also, clamor is a third-declension noun:

• nominative singular: clamor
• genitive singular: clamoris

In foro means in the forum or at the forum/marketplace.

The important grammar point is that in takes the ablative when it shows location:

• in foro = in/at the forum

The noun forum is a second-declension neuter noun:

• nominative/accusative singular: forum
• ablative singular: foro

A very common contrast is:

• in foro = in the forum (location)
• in forum = into the forum (motion toward)

So the ablative foro shows that the noise is happening there, not moving there.

Because Latin word order is much freer than English word order.

In English, we usually need something like:

• There is a great noise in the forum today!

In Latin, est can come in different places, and placing it at the end is very common:

• Quantus clamor hodie in foro est!

This final position often sounds natural and complete in Latin. It does not add a special meaning by itself; it is just normal Latin style.

Hodie means today, and it is an adverb.

Latin adverbs can often move around more freely than in English. Here it comes after clamor:

• Quantus clamor hodie in foro est!

That placement is perfectly normal. It keeps the sentence flowing and puts today near the middle of the clause. A Roman could move it for slightly different emphasis, for example:

• Hodie quantus clamor in foro est!
• Quantus in foro hodie clamor est!

The basic meaning stays the same.

No. It is an exclamation.

Even though quantus can look like the kind of word used in questions, here the punctuation and sense show that it is exclamatory:

• Quantus clamor ... est! = What a noise there is ...!

If it were a real question, it would ask something like How great is the noise? But this sentence is not asking; it is reacting.

Latin often can omit est, especially in short expressions, but it does not have to.

So both of these can make sense:

• Quantus clamor!
• Quantus clamor ... est!

Including est makes the full clause explicit: there is such a noise. It can sound a little fuller or more complete.

Clamor usually means shouting, outcry, uproar, loud noise, or clamor. It often suggests human noise rather than just any sound.

So depending on context, you might understand it as:

• noise
• shouting
• uproar
• commotion

In a place like the forum, clamor could suggest a busy, loud crowd, people calling out, arguing, or trading.

Yes. Even if the basic meaning is already clear, there are several natural ways to put it in English:

• What a noise there is in the forum today!
• How much shouting there is in the forum today!
• What an uproar there is in the forum today!
• How noisy the forum is today!

That last one is less literal, because Latin has a noun (clamor) rather than an adjective like noisy, but it may be the most natural English in some contexts.