Draws attention to the long-term trends in environmental acidification in areas of base-poor rocks in northern Europe. Secular trends are slow, but more rapid acidification has been induced by people from prehistoric times onwards. Such trends must be recognized when evaluating modern effects such as acid rain. Environmental archaeology may help to test the hypothesis that earlier influences, while increasing acidity, have not resulted in the destruction of aquatic or terrestrial ecosystems, which seems to be the case with acid rain.