The preterite of ser and ir (fui, fuiste)

In the preterite tense, the verbs ser (to be) and ir (to go) are highly irregular but share the exact same forms.

PronounForm
yofui
fuiste
él / ella / ustedfue
nosotros / nosotrasfuimos
ellos / ellas / ustedesfueron

Rely on context to know if someone "went" somewhere or if something "was" a certain way.

When it means "ir" (to go)

When used as ir, the verb is usually followed by a (to) and a destination or action.

I went to the palace yesterday.
Fui al palacio ayer.
Did you go on the excursion with the guide?
¿Fuiste a la excursión con el guía?

When it means "ser" (to be)

When used as ser, the verb often describes past events, followed by an adjective or noun.

The trip to the castle was unforgettable.
El viaje al castillo fue inolvidable.
The monument was fascinating.
El monumento fue fascinante.

Using them together

It is common to see both verbs in the same sentence when sharing travel stories.

We went to explore the monument and it was incredible.
Fuimos a explorar el monumento y fue increíble.