No person shall assemble on public or private property with intent to do an unlawful act or, being assembled, mutually agree or act in concert to do an unlawful act, with force or violence, against the person or property of another or against the peace, or make any movement or preparation therefor. Every person present at such meeting or assembly shall endeavor to prevent the commission or preparation of such unlawful act.
(1977 Code § 46-124)