7 September 1631

Historians are generally agreed that some kind of military revolution took place in the conduct of war during the seventeenth century and one name that stands out above all others in implementing it is Gustav Adolf II, king of Sweden, best known in the Latin form as Gustavus Adolphus. At the Battle of Breitenfeld, north of Leipzig in Saxony, his army had the opportunity to show what his reforms could achieve in one of the major battles of the Thirty Years’ War, a conflict that raked its way back and forth across the German lands from the 1620s to the 1640s. So effective were his tactical innovations that by the end of five hours of exhausting fighting against well over 30,000 troops of the Habsburg Holy Roman Emperor, Ferdinand II, only half of his men had actually seen combat.

Gustavus Adolphus II, the king of Sweden, rides into the Battle of Stralsund in August 1628. The battle marked the start of the successful Swedish campaign against the forces of the Holy Roman Emperor, Ferdinand II. The painting, by Jacob van der Heyden (1573–1645), dates from 1630.

This outcome was possible because Gustavus Adolphus had implemented a number of major changes in the way Swedish forces were conscripted, trained and deployed in the decade before Breitenfeld. The reforms were certainly not entirely original, owing much to the sixteenth-century Dutch military reformer, Prince Maurice of Orange. Gustavus Adolphus took ideas where he could and made them into a system. His Articles of War, read out in 1621, placed great emphasis on military discipline to make sure his army fought as a unit and avoided behaviour likely to undermine that unity. Swearing, drunkenness and desertion were severely punished – indeed, there were forty military offences for which the punishment was death.

His men were trained in musketry and the use of the pike, while cavalry was restored as a truly offensive arm, working in combination with the foot soldiers. His most significant innovation came in the way forces were to be laid out on the battlefield. Gustavus rejected the idea of a phalanx in favour of a long line of brigade-strength units, supported on the wings by cavalry and each with its own mobile artillery. To fight effectively in defence and on the offensive, his army had to drill hard to ensure that movement on the battlefield did not turn into a confusion of men and horses. So important was regular rehearsal thought to be that on the very eve of Breitenfeld the men were ordered to practise their manoeuvres.

The Swedish army was also a conscript army, to which all Swedish communities were required to supply a given number of conscripts. This was essential to supply enough men from a small population to match Gustavus’s large ambitions, though it was eventually to leave some villages almost entirely devoid of men. It was this army, made up predominantly of peasant recruits, that intervened in the Thirty Years War to safeguard Sweden’s interests in the Baltic trade and to protect the coastal territory along what are now the Baltic States.As a Protestant state, Sweden was opposed to the imperialistic ambitions of the Habsburg emperor and his Catholic allies, though this did not stop Catholic France from giving him a substantial five-year subsidy to keep the emperor busy fighting in the east.

A seventeenth-century plan of the Battle of Breitenfeld shows the Swedish army, aided by Saxon forces, inflicting a decisive defeat on the armies of the Austrian general Johannes von Tilly. Swedish success was due to innovations in training and tactics introduced by Gustavus Adolphus II.

In 1630, Gustavus landed in northern Germany with an army of perhaps 50,000 men. He could find few Protestant princes willing to support him, except for the Duke of Brandenburg, but when the Imperial army, led by the Austrian commander Johann Tserclaes von Tilly, undertook an invasion of Saxony, the Swedish army moved south to support the Saxon elector, Johann Georg, whose efforts to remain neutral in the war had finally broken down. Tilly’s forces began the systematic spoliation of Saxon territory in late August 1631. On 2 September, the elector signed an alliance with Gustavus and three days later their two armies, 24,000 veteran Swedes and 18,000 inexperienced Saxon levies, met up some miles north of the Saxon city of Leipzig, which Tilly had just captured.

The Imperial army moved north from Leipzig and on 7 September (17 September in the Gregorian calendar) drew up on a field of Tilly’s choosing near the village of Breitenfeld. The site was mainly flat with shallow undulations, ideal for the Imperial army to deploy the 23,000 infantry in the conventional tercio formation (thick squares of pikemen and musketeers, thirty men deep) and also ideal for the 12,000 cavalry under the command of Count Gottfried zu Pappenheim, drawn up on either wing. The Swedes and Saxons arrayed themselves in two independent formations facing the enemy. The Saxons on the left were organized in a thick pyramid of pikemen and musketeers, with no reserve, but supported on each side by horsemen, a deployment similar to the larger Imperial force.

The Swedish line was unconventional. Their units were spread out in a long line in brigade formation, with a second line of reserves behind. Each brigade was supported by its own mobile battery of nine or twelve guns with the heavy artillery in front. The lines of musketeers were six deep, the pikemen five deep. On each wing was a mix of cavalry and musketeers, with gaps between the infantry to allow the cavalry room to charge through and to retire when the charge was done. Each time they returned, the musketeers let off the next fusillade, giving the enemy no breathing space. The object was to use the arms in combination, increasing both defensive and offensive power.

It may have been the novelty of the Swedish organization that prompted Tilly to destroy the Saxons first. Beginning in early afternoon, the cavalry on his left under Pappenheim assaulted the Swedish right, while the tercios lumbered forward and then turned right towards the Saxons. Tilly hoped to outflank the Swedes on both wings and crush the centre like a nutcracker. Pappenheim immediately discovered the strength of the new Swedish tactics. As he tried to outflank the line, Gustavus stretched it further with the reserves. The Imperial horse found that wherever they went they were met by a wall of musket and artillery fire, interspersed with violent sallies by the Swedish cavalry. On the other wing, however, the Saxons folded up; their cavalry was routed and the pyramid crushed. Johann Georg fled with his battered remnants from the field.

What followed was decisive. Tilly ordered his tercios to turn and crush the exposed Swedish flank, but as they did so, the Swedish commander there, Field Marshal Gustav Horn, rapidly wheeled his entire force at right angles so that his 4,000 men now faced the 20,000 Imperial troops trying to manoeuvre into position. Firing with all his cannon and muskets, Horn ordered his foot and horse to charge the enemy. The tercios were clumsy on the move and were not yet ready to meet an assault; their numbers proved a handicap as they crushed together, unable to use their pikes effectively. Horn brought up reserves as planned from the second line and Gustavus sent reinforcements. The Swedish right had now routed Pappenheim and swung round to seize the Imperial guns, which were then fired on the disordered tercios. They fled in panic, and the elderly Tilly, wounded in the fray, joined the flight.

The battle was an overwhelming vindication of the new tactics of the line developed by Gustavus Adolphus. There were 7,600 Imperial dead, 6,000 prisoners and a further 3,000 who surrendered when the Swedes caught up with them at Leipzig. Tilly lost an estimated two-thirds of his entire army. Swedish casualties amounted to 2,100. Emperor Ferdinand was so alarmed when news reached him that he contemplated flight from Vienna to Graz, or even Italy, but the Swedes did not invade his capital, making instead for Bavaria and the Rhineland to rest and replenish supplies.

In hostile territory, the Swedes proved less disciplined than their king’s instructions suggested, committing regular atrocities against the local population. Gustavus and Tilly did not long survive their memorable duel. Tilly died of tetanus in April 1632 after he had been hit by a cannon ball. Gustavus Adolphus was killed at the Battle of Lützen in November 1632, shot in the shoulder, then in the back, and finally as he lay bloody and covered in mud, shot in the head. His flexible, combined-arms line survived for a while, but like all innovations, it was overtaken by the inevitable evolution of both battle tactics and technology.