Late Roman law, like classical law, denied legal validity to some unions.

As with classical law, most of these prohibitions were based on close kinship or on great disparity in the status of the partners. In late antiquity, however, the number of prohibitions increased, in regard both to kinship and status. And penalties for those disobeying prohibitions based on status are much harsher in the late period, with corporal punishment and even death replacing what had been mostly financial penalties — or simply lack of legal recognition — for non-marital unions in the earlier Empire.