of personnel happens from ages 18 through 21 if secondary education was finished, 22 if High school was completed. Recruitment after age 22 is impossible in the regular army; only auxiliary posts are available. As of 2009, starting salary for Mexican army recruits was $6,000 Mexican pesos (US$500) a month with a lifetime $10,000 peso (approximately US$833) monthly pension for widows of soldiers killed in action. The principal units of the Mexican army are ten infantry brigades and a number of independent regiments and infantry battalions. The main maneuver elements of the army are organized in three corps, each consisting of three to four infantry brigades (plus other units), all based in and around Mexico City and its metropolitan area. Distinct from the brigade formations, independent regiments and battalions are assigned to zonal garrisons (52 in total) in each of the country's 12 military regions. Infantry battalions, composed of approximately 300–350 troops, generally are deployed in each zone, and certain zones are assigned an additional motorized cavalry regiment or an artillery regiment. Regional command The territorial organization of the Mexican Army includes twelve Military Regions (Regiónes militares (RM)). Each RM is commanded by a senior officer in the rank of Divisional General of the General Staff (General de División Diplomado de Estado Mayor), a three-star general. Below the military regions are forty-eight Military Zones (Zónas militares (ZM)). Each ZM is commanded by a senior officer in the rank of Brigade General of the General Staff (General de Brigada Diplomado de Estado Mayor), a two-star general. Operational needs determine how many zones are in each region, with corresponding increases and decreases in troop strength. Each commander of the Military Region is appointed and relieved by the Commander of the Army. Usually on the secretary of defence's recommendation, the senior zone commander is also the commander of the military region containing the military zone. A military zone commander has jurisdiction over every unit operating in his territory, including the Rurales (Rural Defense Force) that occasionally have been a Federal political counterweight to the power of state governors. Zone commanders provide the national defence secretary with socio-political conditions intelligence about rural areas. Moreover, they traditionally have acted in co-ordination with the Secretariat of National Defense (SEDENA) on planning and resources deployment. The commanding officer of a military zone has as at the least an independent infantry battalion under his jurisdiction, but also takes