The North East's coal mining past is an important part of our heritage, but how much do you know about its effect on the area where you live?
At the industry's peak, there were 400 pits, employing a quarter of a million people.
The records of the Durham Miners' Association from that time are held at Sunderland University.
Now for the first time, the whole collection is available on the internet. It is attracting interest from scholars all over the world. Lucy Taylor has been to see it.