Herms performed an apotropaic function in Classical Greece, and were usually placed at physical boundaries such as crossroads, or doorways, as well as in gymnasia, near tombs, and in the agora. By the Roman period, they served largely a decorative purpose, and the herm evolved from being surmounted exclusively with the head of Hermes, to being topped by either janiform or singular busts of other gods, mythical heroes and historical portraits.