for past habits or states, whether continuous or repeated:
• Long ago they built most houses out of wood.
• He always caught the same train.

with periods of time that have finished:
• I read the newspaper this morning. (= it is now afternoon or evening)
• He did a lot in his short life. (= he's dead)

for finished actions with time words like a year ago, last Sunday, last week, yesterday, etc:
• Watson and Crick identified the structure of DNA in 1953.
• The first modern Olimpics took place in Athens more than a hundred years ago.