 Armed forces that are not a part of military or paramilitary organizations, such as insurgent forces, often mimic military organizations, or use "ad hoc" structures, while formal military organization tends to use hierarchical forms.The use of formalized ranks in a hierarchical structure came into widespread use with the Roman Army.In modern times, executive control, management and administration of military organization is typically undertaken by governments through a government department within the structure of public administration, often known as a Ministry of Defense or Department of Defense.