They are stone pillars with a round or square hole in which a wooden gate could be attached. Close to Hutstein you may see one:
According to old folk beliefs, they were not allowed to be moved
because the poor souls who would be hurt lived under the stone.
(Source: Otto Milfait, Elvira Landgraf “The Mühlviertel Language, Customs and Sayings”. And again soul, magic…)