The optimum combination of pike and shot, both as a numerical ratio and as a form of deployment, remained hotly debated in military treatises. Setting aside the numerous theoretical models, essentially only two formations were used in the field. Those adopting the Dutch-style counter-march needed thinner lines and more shot than pike, deploying a ratio of two to one in a ten-rank line by the 1590s [C.E.], with the pikemen in the centre, flanked by equal numbers of musketeers. The Spanish and imperial infantry favoured the larger, deeper formations that had been the norm earlier in the sixteenth century. Their pike were grouped as a central block with always twice the number of men in each line as there were ranks deep, because each man needed twice the amount of space in depth as in width to wield his weapon. The effect was to produce a square block that would be flanked by ‘sleeves’ of musketeers. An additional three to five ranks of light arquebusiers generally lined the entire front to maximize firepower. If caught by a cavalry attack, the musketeers could shelter under the pikes that would stretch over their heads. When attacking enemy foot, the arquebusiers would retire round the flanks once they had fired, leaving the pike free to charge. Spanish and imperial commanders sometimes grouped additional blocks of musketeers on the four corners, which can be seen in many battle engravings from the early seventeenth century. This was simply a formation for deploying and advancing, and the additional shot would fan out towards the enemy to fire, falling back to a less exposed side of the square if the formation came under attack.
The large square formation has become known as the tercio after the term used by the Spanish for their infantry regiments, while the thinner, longer Dutch formation is called a battalion. It has become a historical convention to see the latter as inherently superior to the former, not least because of its association with firearms that have appeared to later generations as obviously more advanced than pikes, weapons first used by the ancient Greeks. This distinction is not accurate, nor does it correspond to sixteenth-century military thinking that drew directly on the ancient world for its inspiration. The deeper block formations offered better all-round fighting ability than the thinner Dutch lines, where each unit relied on its neighbours standing firm or its vulnerable flanks would be exposed if the enemy broke through. Though only the first five ranks of the tercio could fire at any one time, the presence of another ten or more behind stiffened the resolve of those in front, or at least made it harder for them to run away. The unit assumed a more imposing presence on the battlefield; something that was a considerable advantage as it bore down on a wavering foe. In an age of black powder, the battlefield soon filled with smoke, making it extremely difficult for commanders to see what was happening. It was easier to lose control of long thin lines, composed of smaller, but more numerous battalions, than a deployment of fewer, larger tercios. These could be positioned en échelon, or diagonally staggered in chequerboard fashion about 200 metres apart. If one became detached or separated, it was generally large enough to fight on alone until rescued.
There was a trend towards increasing the ratio of shot to pike and to stretch formations into thinner lines that became pronounced in the 1630s, as we shall see later. It was partly related to minor technological advances producing the lighter muskets, and possibly also to pressure from soldiers themselves. Recruits generally preferred becoming musketeers rather than pikemen, who often had to stand under fire without personally being able to retaliate. Pikemen had originally received higher pay and were still seen by officers as more honourable than musketeers. Men who rose from the ranks did so ‘from the pike up’ (von der Pike auf), and not from the musket. Pikemen killed using cold steel, like the traditional knight’s lance, whereas musketeers relied on the devilish invention of gunpowder producing thick clouds of acrid smoke, striking their foes from a distance, rather than looking them in the eye. Pikemen also accused their more lightly equipped colleagues of being more prone to plunder, whereas they could not enter houses with their long weapons—something that clearly had a ring of jealousy to it. Certainly, pikemen were more likely to throw away their weapons if their formation broke, thus becoming defenceless, whereas musketeers could flee still fully armed.
The trend towards more shot around 1590 was also due to the deployment of musketeers in smaller, looser formations to open a battle or to delay an enemy while the rest of the army assembled. Parties of 50 or more musketeers would be pushed out in front of the main line, covered by groups of 250 pikemen as a reserve and rallying point. Such methods anticipated those of 200 years later, but generally disappeared around 1630 with the growing emphasis on massed, disciplined firing by ranks developed by the Dutch and copied by the Swedes. Given the inaccuracy of individual shots, commanders emphasized the volume of fire, and later also its rapidity, culminating in the disciplined firing by platoons adopted around 1700.
— The Thirty Years War, pp. 89-91