One of significant alliances in Jiang Hu is the vast underworld of criminals, assassins, fugitives, robbers, pirates and bandits: many of these were highly skilled fighters, and they often banded together to form locally-based armed organizations. This alliance of the underworld or "Brotherhood of Greenwoods" is called Lulin (綠林). In order to strengthen themselves against opposition, they would recruit from the ranks of dispossessed peasants and boatmen, as well as other members of the Jiang Hu. As their numbers grew, it became necessary to form hierarchies and establish rules to maintain order. Members of the Brotherhood of the Greenwoods swore blood-oaths, maintained their own codes of law and ethics, and communicated with secret codes, signs and languages.