Past Progressive

The Spanish preterite progressive is very similar to the imperfect progressive. Both the preterite progressive and imperfect progressive indicate an action that was in progress in the past when it was interrupted by another event. However, the use of the preterite progressive stresses the fact that the action was completed at the time of the interruption.

Estuve estudiando hasta que llamaste. - I was studying until you called.
Lo vi cuando estuvimos caminando. - I saw him when we were walking (and then we stopped walking).
¿Estuviste leyendo ahora mismo? - Were you reading just now?
Él estuvo trabajando hasta las siete. - He was working until seven o'clock.

The preterite progressive is rarely used in everday Spanish.