Officer of a Spanish Tercio, XVI Century A.D.

A "Tercio" ("third" in english) was a Spanish infantry organization during the Habsburg Spain. They were called "thirds" because they were, in theory, made up originally of 1/3 pikemen, 1/3 swordsmen, and 1/3 of firearms. Although other powers adopted the tercio formation, their armies fell short of the fearsome reputation of the Spanish, who possessed a core of professional soldiers, which gave them an edge that was hard for other states to match. On 24 February 1537 the Tercio de Galeras (Tercio of Galleys) was created, considered the FIRST Marine unit in history. Today, the Real Infantería de Marina (Spanish Navy Marines) consider themselves heirs of this unit.