Article: The Twelve Tables forbade any harmful incantation (malum carmen, or 'noisome metrical charm'); this included the "charming of crops from one field to another" (excantatio frugum) and any rite that sought harm or death to others. Chthonic deities functioned at the margins of Rome's divine and human communities; although sometimes the recipients of public rites, these were conducted outside the sacred boundary of the pomerium. Individuals seeking their aid did so away from the public gaze, during the hours of darkness. Burial grounds and isolated crossroads were among the likely portals. The barrier between private religious practices and "magic" is permeable, and Ovid gives a vivid account of rites at the fringes of the public Feralia festival that are indistinguishable from magic: an old woman squats among a circle of younger women, sews up a fish-head, smears it with pitch, then pierces and roasts it to "bind hostile tongues to silence". By this she invokes Tacita, the "Silent One" of the underworld.

Now answer this question: What forbid harmful  incantations?
Twelve Tables