Post mills are a distinctive type of windmill that has had a long history in England. Today only 47 post mills still survive in England. Evidence from 15 of these where their timbers have been subjected to dendrochronological investigations combined with other sources of evidence helps build a picture of the history of each of these mills. Most mills contain timbers from different historical rebuilding phases, but with the main posts often being the oldest component. Bourn Windmill was the earliest of these (the tree from which the main post was made being felled sometime after 1515) but Nutley and Pitstone mills retain almost equally ancient main posts. Scientific timber-dating methods can help corroborate the historical narrative derived from other evidence, such as documentary sources or inscriptions; however, they can also help raise completely new questions, illuminating stages in the history of a structure that were previously unknown or unsuspected
