Todos asistieron al acto.

Todos is the plural form and means everyone / all of them here.

• todo = everything / the whole thing
• todos = everyone / all (masculine or mixed group)
• todas = all (feminine group)

In Todos asistieron al acto, todos stands on its own as a pronoun, meaning everyone or they all.

Spanish often uses the masculine plural for a mixed group, so todos could refer to a group of men, or a mixed group of men and women.

Because the subject todos is plural.

• todos = all of them / everyone
• asistieron = they attended

So the verb must agree with the subject:

• Todos asistieron = They all attended / Everyone attended

If the subject were singular, the verb would also be singular:

• Todo el mundo asistió = Everyone attended

Asistieron is the preterite tense of asistir.

It is the third person plural form:

• yo asistí
• tú asististe
• él/ella asistió
• nosotros asistimos
• vosotros asististeis
• ellos/ellas asistieron

The preterite is used for a completed action in the past, so this sentence refers to an event that happened and is finished.

No. This is a very common false friend for English speakers.

In Spanish, asistir a usually means:

• to attend
• to go to

Examples:

• Asistí a la reunión = I attended the meeting
• Todos asistieron al acto = Everyone attended the event/ceremony

If you want to assist/help someone in English, Spanish often uses:

• ayudar = to help
• sometimes asistir can mean to assist in more formal contexts, especially like to assist someone medically or technically, but that is not the most common everyday meaning.

Because the verb asistir normally takes the preposition a when it means to attend.

So you say:

• asistir a una reunión
• asistir al acto
• asistir a clase

This is just part of how the verb works in Spanish. It is not optional.

Because in Spanish, a + el contracts to al.

So:

• a + el acto = al acto

This contraction is required.

Compare:

• Voy al parque = I’m going to the park
• Asistieron al acto = They attended the event

But there is no contraction with la:

• a la fiesta
• a la reunión

In this sentence, acto usually means something like:

• event
• ceremony
• official act
• formal gathering

In Spain, acto is often used for a somewhat formal, public, institutional, or ceremonial event.

Depending on context, al acto could be:

• a ceremony
• a public event
• a school function
• an official presentation
• a commemorative act

It does not usually mean act in the theatrical sense here, unless the context clearly points that way.

Yes. That is a very natural translation.

Because todos can mean:

• everyone
• they all
• all of them

So depending on context, possible English translations include:

• Everyone attended the event.
• They all attended the ceremony.
• All of them went to the event.

Yes. In this sentence, todos is the expressed subject.

Spanish often drops subject pronouns because the verb ending already shows who is doing the action. So you could sometimes omit a subject if the context is clear.

But todos is not just a subject pronoun like ellos. It adds emphasis and specifically means all of them / everyone.

Compare:

• Asistieron al acto = They attended the event / Attended the event
• Todos asistieron al acto = Everyone attended the event / They all attended the event

So todos makes the meaning more explicit.

If the group is only women, standard agreement would usually be todas:

• Todas asistieron al acto = All of them attended

If the group is mixed or unspecified, Spanish typically uses todos.

So:

• todos = masculine plural / mixed group
• todas = feminine plural

Yes, Spanish word order is flexible.

The most neutral order here is:

• Todos asistieron al acto

But you could also hear:

• Al acto asistieron todos

That version can sound more literary, emphatic, or focused differently. It might highlight the event first, then say who attended.

In normal everyday usage, Todos asistieron al acto is the straightforward, neutral order.

In standard Peninsular Spanish, it is pronounced approximately:

• ah-see-STYEH-ron

More carefully broken down:

• a as in father
• sis with an s
• tie/tjé-like sound from -tie-
• ron with a tapped Spanish r

A broad IPA transcription is:

• /asiˈstjeɾon/

Also, in much of Spain, the c in acto is a normal k sound:

• acto = AK-to

Yes, but it is not exactly the same.

• asistieron al acto = they attended the event
• fueron al acto = they went to the event

Often the difference is small, but asistir sounds a bit more like attend, while ir just focuses on going.

So:

• Todos asistieron al acto is a very natural choice for attendance
• Todos fueron al acto is also possible, but slightly less formal and more focused on movement

It is fairly neutral, but asistir and acto together give it a slightly more formal tone than some alternatives.

Compare:

• Todos asistieron al acto = somewhat formal/neutral
• Todos fueron al evento = more everyday in some contexts
• Todos fueron a la ceremonia = clear and natural too

So yes, the sentence sounds natural, and somewhat formal because of the vocabulary choice.