The Spanish "tercios" were the first modern European army, understood as made up of professional volunteers, instead of the levies raised for a campaign or the hired mercenaries typically used in other European countries. Over a period of one and a half centuries, their position as the finest European infantry was built upon their professional training and high proportion of "old soldiers" ("veteranos"), in conjunction with the particular elan imparted by the lower nobility who commanded them. In addition, they were the first to effectively mix pikes and firearms (arquebuses).