Трое пришли вместе.

Трое is a collective numeral, while три is the ordinary cardinal number three.

In Russian, collective numerals like двое, трое, четверо are often used:

• for groups of people, especially when no noun is stated
• with certain plural-only nouns
• sometimes for mixed-gender groups

So Трое пришли вместе is a very natural way to say Three people came together.

If you used три, you would normally expect a noun:

• Три человека пришли вместе.

Without a noun, трое sounds much more natural here.

Трое is a collective numeral in the nominative case.

It functions as the subject of the sentence, like three people in English.

So in:

• Трое пришли вместе

трое = three of them / three people

It does not name the people directly; it just gives the number as a group.

Yes, in a sense. Russian often leaves the noun unstated when it is understood from context.

Here, трое usually implies something like:

• трое людей
• трое человек
• трое из них

But Russian does not need to say the noun explicitly if the meaning is clear.

So the sentence is complete as it stands.

Because the subject refers to three people, so the verb is plural.

• пришли = came (plural, past tense)

Even though трое may look unusual to an English speaker, it still refers to more than one person, so the verb agrees in the plural:

• Трое пришли not
• Трое пришло

In Russian past tense:

• singular verbs show gender: пришёл, пришла, пришло
• plural verbs do not show gender: пришли

Since трое is plural in meaning, the verb is plural, so no gender is shown.

That means Трое пришли вместе does not tell you whether the group was male, female, or mixed. You only know there were three people.

Вместе is an adverb meaning together.

It describes how they came:

• пришли вместе = came together

It does not change form here, and it does not agree with anything.

Because the two words express different ideas:

• трое = how many people
• вместе = in what way they came

So:

• Трое пришли = Three came.
• Трое пришли вместе = Three came together.

The second sentence adds the idea that they arrived as one group, not separately.

Usually, by itself, три sounds incomplete here.

Russian strongly prefers:

• Три человека пришли вместе = Three people came together. or
• Трое пришли вместе = Three came together.

So if there is no noun, трое is the better choice.

It is the past plural form of прийти, which is a perfective verb.

That means it focuses on the completed action of arrival:

• they arrived / they came

The basic present/future pair is:

• приходить = to come, to be coming, to come regularly or repeatedly (imperfective)
• прийти = to come, to arrive (perfective)

So пришли means they actually arrived.

Not for absolutely everything.

Трое is especially used for:

• people, especially when speaking of a group without naming the noun
• children
• mixed groups
• some nouns that naturally go with collective numerals

But you would not use it in every situation. For many ordinary nouns, Russian prefers три:

• три стола = three tables not normally
• трое столов

So трое is natural for people, but not as a general replacement for три.

It sounds completely normal.

A sentence like Трое пришли вместе is standard, natural Russian. It is not especially literary or old-fashioned.

In everyday speech, Russians often use collective numerals this way when talking about people:

• Двое ушли.
• Трое пришли.
• Нас было четверо.

Yes. Russian word order is flexible.

The neutral order here is:

• Трое пришли вместе.

But other orders are possible, depending on emphasis:

• Вместе пришли трое. = It was three who came together.
• Пришли вместе трое. = Three came together.

The basic meaning stays similar, but the emphasis shifts.

It is in the nominative case, because it is the subject of the sentence.

You can tell because it is the thing performing the action:

• трое did the coming

So:

• Кто пришли вместе? — Трое.

It means exactly three.

Трое is precise: a group of three.

If Russian wanted to say something less exact, it would use different wording, such as:

• около трёх человек = about three people
• человека три = about three people / three or so people

But Трое пришли вместе means exactly three people came together.