Board Thread:Skyrim/@comment-12599067-20130928060857/@comment-80.216.214.210-20131003102240

Lord Hadron wrote: The Reachmen didn't invade on an already inhabited Reach, inhabited by Nords. Not quite no but almost, Reachmen are a mixture of Bretons and Nords.

Therefore it follows that they couldn't have existed anywhere before Nords nor Bretons for that matter.

http://elderscrolls.wikia.com/wiki/Forsworn

"The intermingling of Bretons and Nords in the region has created a regionally distinct lineage of Bretons called "Reachmen".