The Portuguese Army has its remote origins in the military forces of the County of Portugal that allowed its ruler, Afonso Henriques, to obtain its independence from the Kingdom of León and to enlarge its territory in the 12th century.

The victory of the Portuguese forces in the Battle of São Mamede, on 24 June 1128, is considered the seminal event for the foundation of an independent Portugal, leading to Afonso Henriques to style himself as Prince.

The Portuguese ground forces of that time were initially formed by military contingents provided by the landlords (lords of the manors and of the Church), called the mesnadas.

These forces also included bands of irregular riders (latrones) of some warlords, which attacked the moor fortresses by surprise, usually taken advante of the night or of the bad weather.

[2] With the start of the maritime expansion of Portugal in the 15th century, the country's land forces focused on overseas campaigns intended to conquer new territories in Africa, Asia and the Americas, that would form the Portuguese Empire.

The advanced organization of the Portuguese forces, however, was not sufficient to avoid the disastrous defeat at the Battle of Alcácer Quibir with the death of the young and childless King Sebastian.

However, for merely tactical purposes, the companies of horse were occasionally grouped in temporary formations (troços), each under the command of a commissioner general (senior officer of cavalry).

In 1790, Queen Maria I decreed the creation of the Academia Real de Fortificação, Artilharia e Desenho (Royal Academy of Fortification, Artillery and Drawing), in Lisbon, for the higher education and training of the Army officers.

Under French occupation, the Army was disbanded and its most important units were integrated into the Portuguese Legion raised by order of Napoleon, that would fight for him in the campaigns of Germany, Austria and Russia.

The military resistance to invaders began to be carried away mainly by the initiative of the Militias and local Ordenanças, which launched a guerrilla war on the rearguard of the French forces, managing to cut their lines of communications and to isolate many of their units.

In 1809, following the Battle of Corunna, the Portuguese Army was reconstituted under the initiative of the Secretary of War Pereira Forjaz and re-trained by the British under the direction of Lieutenant General William Beresford.

With the end of the Peninsular War, the Army of Brazil is reinforced with military contingents sent from Portugal, one of the most important of these being the Division of Royal Volunteers, commanded by General Carlos Lecor.

It started to be raised from the military units stationed in the Azores (the first portion of the Portuguese territory under Liberal control), including the elite 5th Caçadores Battalion, that had been deployed to garnish the Fortress of São João Baptista in Terceira island.

After the gradual stabilization of the Constitutional Monarchic regime after the Liberal Wars and with no imminent perceived immediate threats against the Portuguese European territory, the Army will focus on internal security duties and in the organizations of military expeditions to overseas.

Until the 1840s and to face the internal troubles caused by the political instability that followed the Liberal Wars, the Army continued to be reinforced with units of volunteers, generically referred as the "national battalions".

So, most of the Army units were frequently requested by the local administrative authorities to maintain public order and to perform other police duties, employing in these services an important part of their personnel.

Despite receiving few popular and military support, the revolutionaries manage to prevail, much thanks to the passive attitude of the Army and its reluctance in suppressing the uprising, with the Constitutional Monarchy being overthrown and the republic being proclaimed on 5 October 1910.

The CEP was deployed to France in the early 1917 and – although almost being destroyed in April 1918, in the Battle of the Lys – it continued to fight on the Western Front until the armistice brought an end to World War I.

The Military Aeronautics arm – although continued to be administratively part of the Army – gained a high level of operational autonomy, starting to have its own central command, what transformed it into an almost separate branch of service.

During World War II, to deter a possible invasion of the Portuguese islands and overseas territories, the Army had to send several military expeditions to reinforce the local defense forces.

The defense of the Azores was crucial as these islands were planned to serve as retreat point and base of the Portuguese Government in case of an enemy occupation of Continental Portugal.

With the creation of the roles of Minister of National Defense and Chief of the General Staff of the Armed Forces on 1 August 1950, a unified chain of command for the then existing two branches of services (with the third one being added in 1952) was established.

However, until the 1960s, the Army high command will show an aversion against the existence of special units, causing the Assault Sappers to be disbanded and the Paratroopers to be fully transferred to the Air Force (where they stayed until 1993).

In Angola and Mozambique, this structure was designed to allow the raising of entire field divisions to be deployed to European Portugal in case of a conventional warfare with the Warsaw Pact.

The main operational formation was now the new 1st Independent Composite Brigade, a mixed mechanized and motorized infantry force, based in the Santa Margarida Military Camp, maintained in a high state of readiness with most of its units permanently raised.

There are two Military Zones (Zonas Militares): The end of the Cold War and the consequent reduction of the threat of a conventional warfare in Europe brought the refocus of the Portuguese Army.

Since the end of the 20th century, the Portuguese Army participated with national deployed forces in numerous foreign operations, including in Angola, Mozambique, Bosnia and Herzegovina, Kosovo, East Timor, Iraq, Afghanistan and Lebanon.

The military regions and zones continued to be responsible for keeping territorial defense brigades and battle groups, mostly maintained only in cadre strength in time of peace.

Operationally, each of the three brigades had a similar organization that included three maneuver (infantry / armoured) and one field artillery battalion, engineering, signals and services companies, an armored reconnaissance squadron and an anti-aircraft battery.

They include units, establishments and bodies divided by the areas of obtainment and administration of human resources, of readying of forces, of logistical support, of teaching and training and of divulgation and preservation of the military culture.