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The Spanish “Tercios” were the elite military unit that the Spanish Empire used to build their success and military prowess during the XVI century.

But how did they come to be?

What made them legendary?

Which were the first battles that consecrated them as one of the finest military units the world has ever seen?


The word “Spain” will be used in this article referring to the Crown of Castille and the Crown of Aragon, and later, to the Spanish Empire or Catholic Monarchy, as it would be known. It is not however the correct term, but it will be used nonetheless for simplicity and to avoid confusion.
Later in the article the word “Imperial” will be used, referring to the Spanish and German troops who fought together since Charles was king of Spain and Emperor of the Holy Roman Empire.

Introduction. What does the word “Tercio” mean?

Literally, the word “Tercio” means a “third part of”, this is, the third part of Spanish forces located in a certain domain or region. Officially, this word appeared in 1536 with the Orden de Génova (Ordinance of Genoa), which referred to three-thirds of the army that were located in Two Sicilies, Lombardy and Málaga. It was used initially to distinguish certain fractions of the Army that weren’t necessarily different from the usual infantrymen and tactics that were used for centuries. Later in time, the word “Tercio” would be given its own identity, representing a new and modern concept of infantry that revolutionized the medieval battle doctrines that determined how footmen were supposed to engage in combat, including equally revolutionary tactics and armament that would give the Spanish “Tercios” their glory and fame as an unstoppable and conquering powerhouse.

Tercios in the Battle of Rocroi, 1643

Precedents. How did the Spanish “Tercios” come to be?

Contrary to popular belief, the Spanish Tercios were moulded in Spain by the Catholic Monarchs ( King Ferdinand II of Aragon and Queen Isabella I of Castile). The more common version is that they were created by Gonzalo Fernández de Córdoba, nicknamed the “Great Captain” during the Italian Wars, being Gonzalo the most trusted general of the Catholic Monarchs. The two kings, once the Reconquista ended, decided to push for military reforms in their army, specifically in the infantry branch since Spain had developed a strong infantry prone tradition during the war against the Muslims. Spanish infantry was already strong and numerous in comparison with many European nations, yet the Catholic Monarchs thought they needed to update them to stand the test for the new challenges ahead, like the war against France for hegemony in Italy.

Because of this, they decided to adopt the Swiss art of warfare, this is, an infantry dominated by pikemen. Swiss pikemen often served as mercenaries to other European nations and soon proved their worth, since many nations still gave cavalry a protagonist role in the battlefield, being effectively countered by the long pikes that the Swiss held with lethal precision. This system, also mastered by the German Landsknechts, found a natural home in Spain, a country with a centuries-old tradition of infantrymen and a long-standing rivalry with France, whose famous heavy-shock cavalry was known and feared all around Europe.

Though influenced at first by the Swiss art of warfare, the Spanish Infantry was then divided into several units, which added several innovations of their own: Firstly, the newly incorporated pikemen; Secondly, squires, armoured and shielded soldiers that wielded swords and held a protective role towards the skirmisher line; Thirdly, crossbowmen, the default range unit in most of the European armies with some notable exceptions (For example, English longbowmen); Lastly, riflemen, soldiers that wielded the newly created Spanish “Espingarda”, one of the first rifles in European history. This was the Army composition that Spain had during the defence of the Rousillon during the First Italian War, but was soon to be changed. 

During the Second Italian War (1499-1501), the Catholic Monarchs sent reinforcements to Gonzalo Fernández de Córdoba, who still battled the French in the Italian Peninsula. This new army of 3.042 infantrymen and 600 horses would demonstrate the metamorphosis that the Spanish Army was suffering during this time period since, after only a couple years, its composition was again changed. The more “medieval” type units, such as squires, crossbowmen and spearmen, had been significantly reduced in numbers, the first one being entirely removed and the last one morphed into halberdiers, whilst the pikemen and riflemen grew both in numbers and importance.

The attention and development that the Spanish put on riflemen was one of extraordinary foresight, having riflemen composing one-fourth of the Spanish reinforces sent to Italy. In fact, Spain was the first country to invest heavily into gunpowder weapons before any other European nations, which gave Spaniards a cutting edge on the battlefields (France wouldn’t incorporate arquebusiers in their army until 1525, whilst longbows would still be used in England until 1595, who wouldn’t have a significant number of riflemen until 1580). 

In 1504 the Catholic Monarchs ordered the reorganization of the “new infantry”, with the creation of companies, that combined pikemen (⅔ of the company) and riflemen (⅓ of the company), commanded by a captain. The protagonism of infantrymen was showcased in the Spanish offensive against the Berber city of Oran, where an army of 11.000 infantrymen and only 700 horsemen was sent to take the city. 

Aguila bicéfala Carlos V
Imperial banner of Charles V that incorporates his Spanish, Austrian, Burgundian and Imperial posessions

The official birthdate of the “Tercios” would come in 1536, when Emperor Charles the I of Spain and V of the Holy Roman Empire baptized this renovated Infantry. However, the reason why Historians include battles that came before that in the “Tercios” sheet is because said date only marks the year in which the word “Tercio” was used to define a military unit that already existed for a few decades. The armament and tactics innovations occurred before 1536, so It could be considered as if the “Tercios” already existed before 1536, but were not yet known as such. For this reason, the Battles of Pavía (1525) and Bicocca (1522) are considered as the first great battles in which the Spanish “Tercios” appeared.

Organization and Armament: What made the Spanish “Tercios” special?

Having already established that the end of the XV century brought to Europe a new and revolutionary idea of warfare, that broke with the Medieval tradition, now it’s the time to clarify why the Spanish “Tercios” were more efficient in battle than other European infantries, like German Landsknechts or Swiss pikemen.

Whilst these military units also adopted the pike as a way to counteract the devastating power of cavalry charges, doing it even before the Spanish infantry ever did, they didn’t quite invest as much into gunpowder, something that was greatly pursued by Spanish kings and generals for decades up to this point.

Obviously, pikes are horses greatest enemy, so traditional cavalry charges couldn’t do a thing to an advancing Spanish force, whilst enemy infantrymen were shot mercilessly by arquebusiers, who wielded primitive but effective rifles, especially against a slow-moving infantry force such as a pike formation. So if cavalry and infantrymen are at a disadvantage, what is left to beat the “Tercios”? Since the Spanish were the first to invest into gunpowder rifles, and to also modernize the first ones ever made, it was almost impossible to win a skirmish fight at a distance. Artillery, though renowned for its inaccuracy during this timeline, proved effective against the tightly bunched Spanish Tercios, but that same inaccuracy proved to be an unreliable system to win battles against the “Tercios”, especially since Spanish cavalry, even though few in numbers and still “Medievalized”, rapidly moved to attack the enemy artillery once the battle started, and the Spanish also had artillery pieces of their own.


Armament wise, the “Tercios” were unique in combining a simple and ancient weapon such as the pike (5,40 meters long) with the modern and revolutionary arquebus. Halberds were used only by company sergeants and by the pikemen that had to defend the arquebusiers in battle, whilst swords were used by every soldier on the battlefield, yet they lacked the tactical importance that pikes and arquebuses had. In 1567, the Tercios that fought in Flanders incorporated several companies of musketeers, that wielded the world-famous muskets, which were heavier than arquebuses and had a slower rate of fire, but they had a greater calibre and range, which allowed musketeers to severely punish approaching enemy formations. 


The “Tercios” were organized as infantry units composed by twelve companies, of both pikemen and arquebusiers, that went up to 3.000 men. The number of soldiers and companies would be however changed constantly during the centuries to come. They soon realized that they had to come up with an effective battleplan to combine their four greatest weapons, since they had many flaws individually.

Pikes were helpless to repel enemy fire whilst being very effective against enemy cavalry and at keeping the enemy infantry at bay. Halberdiers were much more mobile since they didn’t have to rely on compact formations to make use of their weapon, but the shorter range of the halberd against the pike made them useless against enemy pikemen, who were the undisputed champions of the battlefields. Musketeers and arquebusiers could easily destroy the slow-moving pike formations, but were hopeless against cavalry and in melee fights against enemy infantrymen, whilst also needing a lot of space to fire in waves, so they could offset their low fire rate.

As a way to minimize the disadvantages of every weapon and improve their combined efficiency, the Spanish created the “Escuadrón” or Squadron, that was divided as follows. The pikemen adopted a square or rectangle formation, supported by arquebusiers (and later, musketeers) located on every side of the pike square. These arquebusiers were placed outside of the pike square when the battle started, but always in range of the pikes in case enemy cavalry tried to take them out, and after firing on the approaching enemy, immediately retreated inside the square to keep shooting. The four corners of the square were also manned by arquebusiers, forming the “mangas” or sleeves, who had to support the pike line when required.

This battle plan was viewed much like a city wall: Pikemen were the wall that prevented the enemy from getting in, whilst arquebusiers stayed on the ramparts shooting down any enemy that tried to approach the wall.

Conquest of the Azores of 1583. Pikemen forming a rectangle formation, with the arquebusiers at pike range.

The baptism of fire: Battles of Bicocca and Pavia

Franco-Spanish tensions: Coronation of Charles as Emperor of the Holy Roman Empire.

After four years of peace between Spain and France, tensions started again in 1519, when the Emperor of the Holy Roman Empire, Maximilian I, died and left his Empire to his grandson Charles, already King of Spain since 1516, and bribed the prince-electors to vote for Charles as Emperor. However, the French King Francis I, a connoisseur of the election process that was required to become Emperor of the Holy Roman Empire, presented himself as a candidate to receive the Imperial crown, counting with the support of the Pope and offering an even bigger bribe to the prince-electors.

However, the latter were intimidated by Charles, who moved his army outside of Frankfurt, the city where the election was taking place, and decided to vote Charles as the new Emperor. This way, Charles the I of Spain and V of the Holy Roman Empire became the most powerful monarch in Europe with only 20 years of age. Needless to say, this event greatly upset the French king, who immediately started to prepare his forces to strike, fearing that time would only widen Charles’s power and authority.

French reaction: Italian War of 1521-1526. 

Although called “Italian War of 1521-1526”, the conflict started with the French invasion of the Spanish Lowlands, that quickly stagnated and came to nought. After some minor Spanish victories in the Franco-Spanish border, the Duchy of Milan, that was under French rule, was attacked by Imperial forces, forcing the French governor to retreat. Reinforced with 15.000 Swiss mercenaries, the French decided to attack the Imperial camp located in Bicocca, putting the “Tercios” for the test in their first major battle, that ended up being a slaughter.

The Battle of Bicocca

The French realized that flanking the camp was impossible since both flanks were protected by marshes on the East and a deep ditch on the West, whilst the North of the camp (From where the Franco-Swiss forces had to attack) was protected by a sunken road. The north side was reinforced with ramparts and stakes. The Spanish Tercios and German Landsknechts waited from their entrenched positions as the Swiss charged open-field, being mauled down by Spanish artillery. After losing 1.000 men and finally reaching the sunken road, the Swiss found that the ramparts were manned by 4.000 Spanish arquebusiers, that shot at them in rows mercilessly, effectively killing around 3.000 Swiss mercenaries. The few Swiss captains and companies that did manage to climb the ramparts, found that the Landsknechts had taken positions in front of the arquebusiers and slaughtered the Swiss.

In less than an hour, close to 3.000-4.000 Swiss pikemen were killed, whilst not a single casualty was reported on the Imperial side, except for one single Spanish soldier that was kicked to death by a mule. The Swiss packed their bags and left the French Army, that was quickly forced to retreat. Although the Battle of Bicocca wasn’t a decisive victory for the “Italian war of 1521-1526”, It had huge importance, since it was the first major French defeat of the war and the battle that crushed the fame that Swiss pikemen had as fearless mercenaries. To this day, Bicocca is used as a word that means “easy to gain” in Spanish and “house in ruins” in French. 

Battle of Pavía

The decisive battle of the war would come at Pavia. After the French defeat in Bicocca and the Spanish failed siege over Marseille, the French amassed another army and marched again into the Duchy of Milan, claimed by France as her rightful land. The French army, commanded by Francis I himself, moved with such decisiveness that the Spanish were forced to cede more and more land, to the point that even the city of Milan was taken by the French. The disorganized Spanish army was divided and sent as garrisons to the neighbouring cities, and waited for reinforcements. Francis I realized that he couldn’t waste a lot of time sieging the dozens of strongholds and cities that surrounded Milan, so he decided to move against the most important target: Pavia.

The city was manned with the largest Imperial garrison in the area, 6.000 men, that could become a menace if the French decided to bypass the city and keep their advance south. The siege of Pavía started in 1524, and by 1525, the situation was desperate for the defenders. The French established a blockade, preventing the defenders from getting more supplies, but the greater problem was the lack of money to pay the troops, with the German mercenaries that aided the Spaniards in the defence threatening to mutiny. In 1525, an army of 20.000 men came to aid the city, facing a French army of similar numbers that fielded roughly the same amount of infantrymen, but a larger number of horsemen and cannons.

The Spanish took the initiative and moved around the French flank during the night, so they got closer to the city whilst also blocking the French from the supplies that came from Milan. Francis I proved to be equally as audacious and readied his men for battle, convinced that his superior artillery and heavy shock cavalry could win him the day. 

Thinking that the Imperial infantrymen were wavering under the overwhelming firepower of his artillery, Francis I lead a daring charge with his elite cavalry against the Spanish vanguard, easily defeating the Spanish cavalry and forcing them back. However, cavalry wasn’t the “forté” of the Spanish “Tercios”, and a force of arquebusiers managed to surprise the French cavalry whilst they were still regrouping after their victorious engagement against the Imperial horsemen and decimated them. The Spanish cavalry then charged back at the disorganized and confused French lines and exterminated their cavalry. In one swift move, the Imperial army managed to destroy the famous heavy shock French cavalry with minimal losses.

Imperial infantry, who Francis I thought wavering under the fire of his artillery, quickly advanced to engage the enemy cannons, since Francis charged without waiting for the rest of his army to reach his position. Ironically, the French sent their mercenary Landsknechts to face off the advancing Imperial Landsknechts, who hated their French-serving compatriots for betraying their rightful lord, Emperor Charles V. After a ferocious engagement, the Imperial Landsknechts put their compatriots on the run, whilst the Spanish did the same with the Swiss mercenaries who were also employed by Francis. Spaniards and Landsknechts quickly advanced to aid the garrison of Pavia, who made a move and attacked the French troops placed in front of the city.

After being mauled by the Spanish arquebusiers, and being left alone after the defeat suffered by their mercenaries and horsemen, the French infantry quickly dropped their weapons and retreated, leaving behind close to 15.000 dead and their king captured and in shackles. The Imperial forces lost around 1.000 men (although some authors lower that number up to 500). The Spanish arquebusiers proved again that their mobility and firepower was a decisive factor in the battle, much like in Bicocca, decimating the legendary French cavalry and Swiss pikemen.


All in all, the Spanish Tercios were one of the most powerful military units of their time, and the two battles described in this article are just a fraction of the long list of wars and military encounters that the Tercios had to face in order to expand or defend the already huge Spanish Empire. In further articles, we will view and learn about other famous wars and battles in which the Tercios partook.


  • Albi de la Cuesta, Julio (2017) De Pavía hasta Rocroi: Los Tercios Españoles, Desperta Ferro, Madrid. 
  • Quatrefages, René (1979) Los Tercios españoles (1567-1577), Fundación Universitaria Española, Madrid.
  • Belloso Martín, Carlos (2010) La Antemuralla de la Monarquía: Los Tercios españoles en el Reino de Sicilia en el Siglo XVI, Ministerio de Defensa, Madrid.
  • Pita da Veiga, Gabriel (2020) “La prisión del rey de Francia”, Revista de Historia Militar, vol 127, pp. 143-192.
  • https://www.1898miniaturas.com/en/article/spanish-tercios-organization-tactics-thirty-years-war/

Michele Leandro Polacci

History graduate at Málaga University (UMA). Passionate about History since a very early age, and looking forward to sharing that same passion.


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