The common law did not consider possession a constituent element of the actus reus based on the idea that possession was not equated with the external manifestation of mens rea. However, with the development of the criminal law, with an ever-increasing volume of criminal offences on the statute books, the concept of possession as an element of the actus reus became intrinsically important in the construction of criminal liability. Although it is passive rather than active possession is an element of certain offences that prohibit the mere possession of objects or substances considered harmful to the public such as illegal drugs, child pornography, offensive weapons, unlicensed firearms, and theft offences.