The Spanish Tercio was a 16th century large infantry regiment, which consisted of 3,000 pikemen, swordsmen and arquebusiers in a mutually supportive formation. Also known as the Spanish Square, it was similar to the Swiss square. It was widely adopted across international lines and dominated the battlefields for more than a century. Spain had fought an eight-century long war against the Muslims Arabs that had invaded Spain at the beginning of the 8th century. By 1492, the Spaniards, united under Isabella I of Castile and Ferdinand II of Aragon, had emerged victorious with a highly professional tough fighting machine.
The Spanish Tercio formed the backbone of the most successful army in the world. It contained pikes, some sword-and-buckler men, and light firearms organized under captains and colonels. Spain had an efficient organization for recruiting from its own provinces and keeping these units "topped up." The endless campaigns in Italy and the Low Countries made them formidable troops, with high confidence and esprit de corps.
The Tercio was composed largely of professional soldiers with superior discipline and fighting spirit, and were well known on the European battlefield for their near-invincibility in combat during the 16th and 17th centuries. The Spanish Tercio formation was 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 Francis I was captured by the Spaniards.
About 3,000 men of a Tercio were armed with an assortment of weapons to deal with any enemy they encountered on the battlefield. Approximately 1,500 of them were equipped with pikes, 1,000 kept the ancient short sword and javelin armament, and the remaining 500 were armed with arquebuses of the best and most portable type. In battle the pikemen formed squares with the sword-and-javelin men inside, and the arquebusiers, together with field artillery, assumed positions in between the squares to gain the best angles of fire on any enemies approaching the tercio square.
In front of the square formations they would dig ditches or other fortifications to further disrupt a cavalry charge, against which they were essentially invulnerable. Even in battle against an opposing force of pikemen, the tercio had the upper hand in terms of ranged firepower with the arquebusiers causing devastating casualties amongst the tightly packed pikemen as well as the fact that a pikeman, needing both hands to wield his pike, was essentially defenseless against the tercio swordsmen.
[...] The Spanish Marines, or Infantería de Marina, is the oldest marine corps in the world. It was created in 1537 by Charles I, when he assigned the Naples Sea Old Companies to the Mediterranean Galley Squadrons. Philip II settled today’s concept of Landing force; that is to say pure Naval Power projection ashore by forces coming from ships and able to fight, not been downgraded by the fact of been based on board. This is the period of the famous Tercios. [...]