Does map.root need to be the last named route in routes.rb?

If I put

  map.root :controller => 'blah'

before any of my other named routes, I get the error:

ActionController::MethodNotAllowed

  Only get, head, post, put, and delete requests are allowed.

but if I put it after all of my other named routes, it works fine.

Is this normal behavior and why?

Thanks,
Wes