Tercio The Battle of Pavia ( 1525 ) Tercio ( Also known as `` Spanish Tercios '' ) was a term used by the Spanish army to describe a mixed infantry formation of about 3 , 000 pikemen and musketeers , sometimes referred to by other nations as a Spanish Square . It was a formalization of the organization and fighting techniques that had been developed principally by the brilliant general , Gonzalo Fernández de Córdoba , during the Italian Wars . It marked the transformation of medieval military institutions into the early modern combined-arms army with a focus on infantry . This completed a process that was already underway in the time of the 100 Years War . Tercios , consisting largely of professional soldiers with superior discipline and fighting spirit , were well known on the European battlefield for their wellnigh-invincibility in combat during the 16th and 17th centuries . The formation was often feared by enemy troops because of the legendary determination of its soldiers in combat – its reputation was fully established at the Battle of Pavia ( 1525 ) , in which the French king was captured ; the prospect of being thrown into battle against the Spanish tercios was even known to lead to desertions in opposing forces . Although other major powers adopted the formation , their armies fell short of the fearsome reputation of the Spanish . That army , however , was not made up entirely of Spaniards , but was `` an army of different nations '' , many of the troops being mercenaries ( landsknecht ) from Germany , Italy and the Walloon territories of the Spanish Netherlands . But the Spanish formed the core , noted by others for their superiority in discipline and professionalism . Their professionalism was displayed in the Battle of Rocroi ( 1643 ) , when the German and Walloon tercios fled from the battlefield , while the Spanish stayed on the field with their commander , absorbing three cavalry charges by the French , before the fourth finally broke their formation with the assistance of artillery . Within the tercio , ranks of pikemen arrayed themselves together into one large block ( carré ) . The musketeers were usually split up in several mobile groups ( mangas ) and deployed relative to the carré , typically with one manga at each corner . By virtue of this combined-arms approach , the formation simultaneously enjoyed both the rigidity of its heavy infantry and the long-range firepower of its musketeers , making it an ideal defense and offense formation . The end of the dominance of the tercio came with the Spanish defeat by the French at the previously-mentioned Rocroi in 1643 . In the late 17th century , the Spanish army abandoned the then-obsolete tercio in favour of the more flexible system of battalions and regiments , based on the French model . This new system of fighting in linear formation was promoted by the Swedish king Gustavus Adolphus , and would dominate the 18th century battlefield . The linear formation relied on shock force more than any other element : soldiers would fire their muskets simultaneously , demoralizing the enemy force . The tercios proved inadequate to withstand this new formation , which was more organized and sustained fewer casualties by cannon fire . Today , the Spanish Legion and the Spanish Marine Corps still uses the tercio as its largest unit designation . See also Ferrol City and Naval Station in North-western Spain External links The Spanish Tercios : http : //www.geocities.com/ao1617/TercioUK.html Renaissance Armies : The Spanish ( myArmoury.com article ) Alonso Pita da Veiga the most heroic Spaniard at the Battle of Pavia ( Italy ) 1525 Non-Official Web of the Modern `` Spanish Marines '' in existence since 1537 few years after Battle of Pavia ( Italy ) 1525 and well before the Battle of Lepanto ( Greece ) 1571 Non-Official Web of the Modern `` Spanish Tercios '' inheritors of those who fought in the Battle of Pavia ( Italy ) 1525 and the Battle of Lepanto ( Greece ) 1571 Categories : Infantry organization | Military unit types | Early Modern warfare In other languages : Català | Español | Français | Italiano | 日本語 