The Spanish Tercios - Legendary War Units

During the Thirty Years War (1618-1648), organic flexibility was one of the basic characteristics of the armies of the Spanish Monarchy, as it had been in the previous century. Tercios were, above all, groups of a number of companies that could be attached or detached at all times. Unlike the French Crown, which in the period 1610-1660 tended to group its veteran troops into units formed entirely by experienced soldiers, the Spanish Monarchy favoured the merge of experienced companies and companies of bisoños (green recruits) in the same Tercio, which guaranteed a good average level in combat units.
The flexibility of the Spanish military model went further, since the same Tercio could fight at the same time in scenarios as different as Brazil and the Mediterranean. This happened when the unit was subdivided into two, one commanded by its maestre de campo, and another by his second in command, the sergeant major. This eventuality occurred in several cases during the Thirty Years War, when Spain had to fight in numerous fronts not only in Europe, but also in America and Asia.
As for the internal organic, an important difference with respect to the previous years was the decrease in the number of troops per Tercio, which fell to an average of between 1000 and 1500 men. In 1633, for example, the Army of Flanders had three Spanish infantry Tercios with 3760 troops in total divided into 51 companies. On average, by then Tercios had between 15 and 20 companies each. Companies were administrative units, usually commanded by a captain and formed by soldiers of three types: pikemen, musketeers and arquebusiers.