A tercio was a military administrative unit of the Spanish Army during the reign of the Catholic Monarchs of Spain and Habsburg Spain in the early modern period. They were the elite military units of
Surrender of Breda, by Velázquez, shows Ambrosio Spinola (at right), commander of a Spanish tercio, receiving the keys to the city from a defeated Dutch general in 1625.
Tercios disembarking, 1583
Schematic depiction of the pikemen's combat drill.
Pike and shot was a historical infantry tactical formation that first appeared during the late 15th and early 16th centuries, and was used until the development of the bayonet in the late 17th century
Tercio
…of Gonzalo Fernández de Córdoba during the conquest of Granada and the Italian Wars in the 1490s and 1500s, being among the first to effectively mix pikes and firearms (arquebuses). The tercios marked a rebirth of the use of infantry forces comparable to the Macedonian phalanxes and the Roman legions. Such formations…
A 16th-century pamphlet showing a mixed pike and shot formation. Pikemen are represented by the letter "p", the two "winges of shot" by the letter "o". (The letter "h" represents halberdiers.) A group of "loose shotte" has been pushed forward into the front of the formation.
A model of a section of a pike and shot formation from the Thirty Years' War on display at the Army Museum in Stockholm. Consistent (uniform) dress was not common for military troops at the time.
Gari Melchers War Highsmith