For three or more persons, in violent or tumultuous manner, to assemble together to do or attempt to do an unlawful act, or when together to do or attempt to do an unlawful act, or when together, to commit or attempt to commit an act, whether lawful or unlawful, in an unlawful violent or tumultuous manner to the disturbance of others. (See Title B, Chapter 2, § 1.28 or Iowa Code § 723.2.)