On 6 March 1645 a Swedish army under Field Marshal Lennart Torstensson attacked the Imperial army of Melchior von Hatzfeldt in the hills and woods around Jankau, today Jankov in the Czech Republic. In a day of fighting on broken ground the Swedes beat the Imperial wings one after another, captured Hatzfeldt and thousands of his men, and destroyed the Bavarian cavalry. Swedish accounts date the battle ten days earlier, to 24 February, because Sweden still used the Julian calendar.
A march into Bohemia
While peace talks were opening in Münster and Osnabrück, Sweden tried to win as much as it could on the battlefield first. In late January 1645 Torstensson led his army into Bohemia, meaning to join George Rákóczi, Prince of Transylvania, and threaten Vienna itself. Emperor Ferdinand III gathered an army under Hatzfeldt, strengthened by Bavarian cavalry under Johann von Werth and by troops under Johann von Götz.1
For weeks the two armies shadowed each other. On 2 March the Swedes crossed the Vltava near Orlík castle, and Hatzfeldt hurried ahead to block their road into Moravia near the village of Jankau, between Votice and Louňovice pod Blaníkem.2
Sweden used the Julian calendar until the 18th century, ten days behind the Gregorian calendar of the Emperor's lands, which is why Swedish accounts give 24 February.3
Ground that favored the Swedes
Accounts do not agree on the size of the armies. John Rickard of HistoryOfWar.org describes the Imperial and Bavarian force as the larger of the two, but notes that the broken ground kept it from using its numbers, and that Torstensson was able to deal with his enemies piecemeal. The Czech military history project Bellum.cz stresses Torstensson's careful reconnaissance the day before, and his decision to strike the Imperial left from the flank instead of fighting line against line.4
A battle in two phases
On the Imperial left Götz reacted rashly. According to Bellum.cz he attacked with his cavalry, without proper reconnaissance, into a narrow space between dense forest and ponds, where his cuirassiers got stuck and were cut down by Swedish artillery; Götz was killed in the fighting. Werth's cavalry on the other wing tried to work round the forest and was also driven back by Swedish guns.5
By midday the Imperial army was falling back, but Hatzfeldt rallied it. In the afternoon his Bavarian cavalry and part of his infantry attacked again, and some units got round into the Swedish rear. There, instead of attacking, they began to plunder the Swedish baggage, and the Swedes used the pause to regroup and counterattack. A final Swedish attack drove the Imperial army from the field, and the Bavarian cavalry was destroyed.6
The cost, and a road to Vienna
Bellum.cz gives the Imperial losses as almost 4,000 men, with nearly as many taken prisoner, among them Hatzfeldt and five other generals. A German historical marker on the Thirty Years' War at Dinkelsbühl sums it up: Hatzfeldt was captured and the Emperor lost his most important army, which opened the road to Vienna. Bellum.cz adds that Ferdinand III, then in Prague, had to leave the city in haste.7
But the Swedes could not finish the campaign. Their siege of Brno lasted more than three months and failed, which gave the Emperor time to raise new troops and save Vienna. Rickard notes that devastated Bohemia could not feed the Swedish army. The war went on until the Peace of Westphalia in 1648. For the wider age of pike, musket and cannon, see our guide to the greatest battles of the early modern era.8
Note: no reliable figures for the size of the armies are given in these sources, and the losses are estimates.
