The Past Continuous Tense
If ‘be’ is in the past tense (was, were), then the construction is called the past Continuous; for example:
The president was visiting Peru last week.
The past simple and the past continuous are used with reference to past time.
When you are talking about the past, you use the past continuous for actions that continued to happen before and after another action, or before and after a particular time. This is often called the ‘interrupted past’. You use the past simple for the other action.
He was watching T.V. when the doorbell rang
They were sitting in the kitchen when that heard the explosion.
It was 6 o’clock. The train was nearing London.
He was working at home at the time.
She was using my office until I came back from America.