Learn Hardcore Portuguese (Brazil): Chegamos cedo ao teatro, mas a fila para entrar na peça já estava longa. - We arrived early at the theater, but the line to enter the play was already long.

Chegamos already tells you the subject is we (either nós chegamos – we arrived / we arrive).
Adding nós (Nós chegamos cedo ao teatro…) is possible, but it usually adds emphasis or contrast (e.g. Nós chegamos cedo, mas eles chegaram tarde).

So the sentence is perfectly natural and common without nós.

How do I know if chegamos here is present tense (we arrive) or past tense (we arrived)?

The form chegamos is the same for present and simple past in the nós form:

Present: (nós) chegamos cedo ao trabalho. – We arrive early at work.
Past: (nós) chegamos cedo ao trabalho. – We arrived early at work.

In your sentence, context and the rest of the verbs show it is past:

chegamos (arrived)
já estava longa (was already long)

Because estava is clearly past (imperfect), chegamos is also understood as past.

What exactly is the difference between ao teatro, no teatro, and para o teatro?

All three are common, but they express slightly different ideas.

ao teatro = a + o teatro
- Often used with verbs of movement (like ir, chegar) meaning to the theater (destination).
- Chegamos cedo ao teatro. – We arrived early at / to the theater.
para o teatro
- Also used with movement, often emphasizing destination/purpose: to the theater.
- Very natural in Brazilian Portuguese: Vamos para o teatro. – We’re going to the theater.
no teatro = em + o teatro
- Means in/at the theater (location, not movement).
- Estamos no teatro. – We are in/at the theater.

In your sentence, chegamos cedo ao teatro sounds slightly more formal/literary than chegamos cedo no teatro, but both can be heard in Brazil. For standard written Portuguese, ao teatro is a good choice with chegar.

What does cedo mean here, and where can it go in the sentence?

Cedo means early.

In this sentence:

Chegamos cedo ao teatro… – We arrived early at the theater…

You could move cedo a bit without changing the meaning:

Chegamos cedo ao teatro.
Chegamos ao teatro cedo.

Both are acceptable. Placing cedo right after the verb is very common and natural.

What does fila mean, and why not use linha for “line”?

In Brazilian Portuguese:

fila = a line/queue of people or things waiting for something.
- a fila para entrar – the line to get in / the queue to enter.
linha is used for:
- lines in writing, drawings, or on paper
- routes (bus line: linha de ônibus)
- telephone line: linha telefônica

So for a line of people waiting, the correct word is fila, not linha.

Why is it a fila para entrar and not something like a fila de entrar?

The structure para + infinitive is very common in Portuguese to express purpose or function:

fila para entrar – a line to get in / for entering
roupa para lavar – clothes to wash
dinheiro para gastar – money to spend

Using de here (fila de entrar) would sound wrong. De is used in other patterns, like:

medo de entrar – fear of entering
vontade de entrar – desire to enter

For a line to do something, think fila para + [verb in infinitive].

Why is it entrar na peça instead of entrar na + teatro or entrar para a peça?

There are two points:

Preposition with “entrar”
The verb entrar normally takes em for enter (in/into):
- entrar em casa, entrar no teatro, entrar na sala
  Na is em + a, so:
- entrar na peça = enter into the play.
Meaning / focus
entrar na peça focuses on entering the performance/event (the play) rather than just the physical building. It corresponds to English get into the play (as an event).

You could also hear:

a fila para entrar no teatro – the line to enter the theater (building)

Both are grammatically correct; they highlight slightly different things.

What exactly is na grammatically?

Na is a contraction of the preposition em and the feminine article a:

em + a = na
em + as = nas
em + o = no
em + os = nos

Here:

entrar na peça = entrar em + a peça

So na peça means in the play / into the play.

Why is it já estava longa and not já era longa or já foi longa?

Estava (imperfect of estar) is used here because we’re describing a temporary state/situation in the past:

a fila já estava longa – the line was already long (at that time).

Nuances:

estava longa – describes how the line was at that moment (temporary condition).
era longa – more like describing a permanent/characteristic quality (the line was (by nature) long), which doesn’t fit well here.
foi longa – would normally refer to the duration of something (e.g. A aula foi longa. – The class was long), not its physical length in that instant.

So já estava longa is the natural choice for a temporary, ongoing state at the time you arrived.

What’s the role of já in já estava longa?

Já here means already, just like in English:

a fila já estava longa – the line was already long.

This implies:

By the time we arrived (early), the line had already become long.
It adds the idea that you might not expect the line to be long yet.

Why is it longa and not longo? How does agreement work here?

Adjectives in Portuguese must agree in gender and number with the noun they describe.

fila is feminine singular: a fila.
So longo has to become longa (feminine singular) to match:
- a fila longa – the long line
- as filas longas – the long lines
- o filme longo – the long movie (masc. sing.)
- os filmes longos – the long movies (masc. plural)

That’s why the sentence has a fila… estava longa.

Could I use comprida instead of longa for the line?

Yes, you could say:

a fila já estava comprida.

Both longa and comprida can be used for a physically long line. Differences:

longa – more neutral, possibly a bit more formal or “standard”.
comprida – very common in everyday speech; often interchangeable in this context.

In this sentence, both sound natural in Brazilian Portuguese.

How does the conjunction mas work here? Could I replace it with something else?

Mas is a coordinating conjunction meaning but:

Chegamos cedo ao teatro, mas a fila… já estava longa.
– We arrived early at the theater, but the line… was already long.

It introduces a contrast or unexpected outcome.

Possible alternatives:

porém – more formal, often used after a comma:
Chegamos cedo ao teatro, porém a fila… já estava longa.
só que – more informal / conversational:
Chegamos cedo ao teatro, só que a fila… já estava longa.

Mas is the most common and neutral choice.

Can I change the word order, like putting cedo or the clauses in different places?

You have some flexibility in Portuguese. For example:

Chegamos cedo ao teatro, mas a fila para entrar na peça já estava longa.
Chegamos ao teatro cedo, mas a fila para entrar na peça já estava longa.

Both are fine.

You can also move the clauses, though it sounds slightly heavier:

A fila para entrar na peça já estava longa quando chegamos cedo ao teatro.

This last one adds quando (when) and sounds a bit more formal, but it’s grammatically correct. The original order is natural and clear in everyday language.