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Officially, human sacrifice was obnoxious "to the laws of gods and men." The practice was a mark of the "Other", attributed to Rome's traditional enemies such as the Carthaginians and Gauls. Rome banned it on several occasions under extreme penalty. A law passed in 81 BC characterised human sacrifice as murder committed for magical purposes. Pliny saw the ending of human sacrifice conducted by the druids as a positive consequence of the conquest of Gaul and Britain. Despite an empire-wide ban under Hadrian, human sacrifice may have continued covertly in North Africa and elsewhere.

What ruler banned human sacrifice empire wide?
Hadrian