The March Across the Belts (Swedish: Tåget över Bält) was a military campaign waged by the Swedish Empire across the ice between the Danish islands. It lasted between 30 January and 15 February 1658, ending with a decisive victory for Swedish King Charles X Gustav during his first Danish war.
On 5 June 1657, Denmark declared war on Sweden which was under heavy pressure in the Second Northern War against Poland and Russia. Although Charles X Gustav was deeply involved in the conflict with the Polish–Lithuanian Commonwealth, he chose to move the bulk of his army to Jutland and invade Denmark. The king's rapid march surprised the Danish troops, whose main body was forced to retreat to the fortress of Frederiksodde. The Swedes attacked and conquered Frederiksodde on 27 October. With Jutland secured, Charles X Gustav sought to continue his campaign towards Copenhagen on Zealand, but the Danish Straits and the Danish navy obstructed him. Since the 17th century was the coldest during the Little Ice Age, with the winters in Scandinavia being exceptionally frigid, the king planned to take advantage of the weather by remaining in Jutland until sufficient ice had built up to support the weight of his troops, and then carry out a risky march across the ice.
After investigating the ice conditions, the king began his march on 30 January 1658 from Jutland across the strait of the Little Belt to Funen. Swedish troops defeated the Danes at Tybrind Vig and Iversnæs and occupied Funen after a few days. To avert the risk that his troops would be isolated on Funen, Charles X Gustav investigated the possibility of crossing the ice of the Great Belt to Zealand. On 5 February the ice at southern Funen was deemed sufficiently thick, and the king decided to cross to Langeland. He continued through Lolland and Falster and reached Zealand on 11 February. With Swedish troops standing 22 kilometres (14 mi) from Copenhagen on 15 February, King Frederick III of Denmark chose to make an unconditional peace with Sweden, ending the Swedish campaign.
Charles X Gustav's gamble ended with a catastrophic defeat for Denmark. The resulting Treaty of Roskilde, signed on 26 February 1658, was highly favorable for Sweden. Denmark ceded Scania, Blekinge, Halland, Bohuslän, Bornholm and Trøndelag to Sweden. Bornholm and Trøndelag were returned to Denmark in 1660 after Charles X Gustav's failed attempt to defeat Denmark completely in a second war. In its historiography, several historians have highlighted the campaign and the resulting peace treaty as the events that gave Sweden its current "natural" borders. Likewise, the events gave rise to a polarised debate over the role of quartermaster general Erik Dahlbergh in the king's decision to march across the Great Belt.
Background
In 1655, King Charles X Gustav began a campaign against the Polish–Lithuanian Commonwealth to force King John II Casimir Vasa to renounce all claims to the Swedish crown, as well as conquer the Polish provinces of Courland and Prussia. The Swedish Empire would be expanded, while the control of the lucrative Baltic Sea trade strengthened. However, the war against Poland was slow. Despite several tactical victories on the battlefield, including the conquest of Warsaw, Charles X Gustav was unable to bring the war to an end. The Poles resisted the Swedish troops, who were being ambushed constantly by Polish guerrilla units. Poland's neighbors threatened to get involved in the war. Both Austria and the Netherlands sent military aid to Poland, and Sweden's former ally, Brandenburg-Prussia, changed sides during the conflict. In 1656, Russian troops had crossed the border into Swedish Livonia and besieged Riga.
In 1657, Denmark was ready to attack Sweden, seeing an opportunity to tear up the Treaty of Brömsebro signed in 1645, when they were forced to cede to Sweden the provinces of Gotland, Saaremaa, Jämtland and Härjedalen, including Halland for a 30-year period. But the Danish command, led by King Frederick III, realized that they were not strong enough to confront Sweden on their own. Denmark tried to gather allies from Poland, Austria, and the Netherlands, and by summer 1657 the situation seemed very advantageous to Denmark. On 5 June 1657, the Danish fodermarsk Christian Wiborg handed over the formal declaration of war to Governor Erik Stenbock in Halmstad, which later reached Charles X Gustav's field camp in Thorn on 20 June. The Swedish army was involved deeply in the wars against both Poland and Russia, and the Danes were able to use this to put further pressure on Sweden. As an increasingly precarious situation emerged around them, Charles X Gustav and his advisers sought a suitable solution to the Polish conflict. A quick victory over Denmark would strengthen Sweden's position and hopefully dissuade other powers, mainly Austria, from deeper involvement in the Polish conflict.
Campaign in Jutland and the assault on Frederiksodde
Charles X Gustav sought to avoid ending up in a second stalemate, in a protracted war without a decisive opportunity in sight. He marched his army rapidly from Poland through Pomerania, towards Jutland. The king's army numbered about 17,000 men; only 4,000 were Swedes while the majority were foreign mercenaries. By 25 August the Swedish army stood outside the Danish fortress of Frederiksodde, on the east coast of southern Jutland. Smaller Danish forces had been defeated along the way, but no decisive victory had been achieved, and the Danish leadership felt secure in their belief that Frederiksodde would protect the Danish islands. The war took place on other fronts. Swedish troops under Per Brahe the Younger and Gustaf Otto Stenbock fought the Danish troops garrisoned in Scania and Halland, and in Bohuslän and Jämtland during the so-called Krabbefejden ("The Krabbe feud", named after Danish military officer Iver Krabbe). After the inconclusive battle at Møn during the autumn of 1657, the Swedish navy returned to their base in Stockholm for the winter. The Danish navy also prepared to cease operations before the winter. Both parties seemed to agree the stalemate would persist during the cold months.
Charles X Gustav knew that the Swedish army found itself in a vulnerable situation in Jutland and wished to regain the initiative in the war by acting swiftly. On 24 October 1657 during the siege of Fredriksodde, a determined Swedish force led by Field Marshal Carl Gustaf Wrangel unexpectedly assaulted. The fortress fell, and the entire Danish garrison—involving several of the Danish army's best regiments—surrendered. Marshal of the Realm Anders Bille was captured and died a few weeks later. As the Swedes now controlled all of Jutland, the fall of Frederiksodde was deemed disastrous for Denmark, which had lost control to the Danish islands. During the period after the assault on Frederiksodde, the Swedish command felt insecure, fearing an attack from Brandenburg against Swedish Pomerania and then against the army stationed in Jutland. It was urgent to force Denmark to capitulate to prevent the war from turning against them: hence the Swedes set an assault on Copenhagen as their main objective. But to get there, they needed to find a way across to the island of Funen. The Danish troops on the island understood an invasion attempt was imminent.
Ice investigations along the Little Belt
The preparation of a detailed plan for the crossing was delegated to Carl Gustaf Wrangel, who would also prepare for possible Danish landing attempts on Jutland. On 9 January 1658, Charles X Gustav held a military conference in Kiel with his senior officers and civilian officials, including Wrangel, count palatine Philip Florinus of Sulzbach and Margrave Charles Magnus of Baden-Durlach. During the conference, most of its participants agreed the Swedes would conduct a landing operation on Funen, with a small squadron of five warships from Wismar led by skeppsmajor Tönnes Specht. By mid-December 1657, the squadron had assembled in Sønderborg and seized several transport vessels from Vendsyssel and Samsø that were carrying grain to Lübeck. But the ice cover came closer every day, and it was uncertain whether the entire Swedish cavalry could be transferred across the strait. As ice spread quickly and the cold persisted, getting to Funen with transport ships became impossible. This left only one alternative—a march across the frozen Little Belt, the strait between Jutland and Funen. Several conference participants reported ice formations along Jutland's east coast, at Assens' ferry, at Haderslev, and at Flensburg.
Between 22 and 23 January, Charles X Gustav sent orders to his senior officers to investigate the ice around Funen and find a crossing to Ærø, and onward to Funen and Langeland. On 24 January, Wrangel reported he rode on horseback along the coast from Kolding to Frederiksodde and that the water was completely open. The army command deliberated about crossing the ice towards the Ærø strait at Assens on Funen, a good distance south of Frederiksodde. Swedish scouts rode out on the ice east of Øsby and spotted Assens, but they made the assessment the ice was still too weak to cross. Another reconnaissance patrol was dispatched from Als towards Ærø, but they established the strait was open and was filled with ice floes.
On the morning of 26 January, a Swedish patrol of five men crossed the ice to the island of Brandsø, 2 kilometres (1.2 mi) from Jutland's east coast. On the island, they were surprised by 15 Danish horsemen; four of the Swedes were captured, but one escaped and reported the incident to Wrangel. He immediately sent a unit of 50 horsemen and 150 infantry under Adjutant General Friedrich von Arensdorff to the island. On the evening of 27 January, Arensdorff returned and reported the Danish horsemen abandoned Brandsø and fled back to Funen across the ice. The distance between Frederiksodde and Funen was just over 4 kilometres (2.5 mi) at its narrowest point, and 17 kilometres (11 mi) at its widest. Charles X Gustav ordered the occupation of Brandsø with 100 men, later reinforced with an additional 300 men.
On 28 January, Wrangel marched with the cavalry out of Frederiksodde to Hejls close to Hejlsminde Bay, where the rest of the cavalry arrived on 29 January. They planned to start the ice march from a place between the villages of Anslet and Knudshöfft, 6 kilometres (3.7 mi) south of Hejls. On 28 January, Charles X Gustav reached Haderslev and received reports from Wrangel about his route map. The king approved his plan, giving Wrangel permission to begin the march without the king and his troops, provided that the ice was deemed sufficiently thick. The king arrived at Hejls on 29 January: Wrangel had not yet set out. Later that day, a detachment of between 500 and 600 troops was sent across the ice to scout the road to Funen. The force reached the foreland of Iversnæs on the other side of the strait occupied by Danish troops. They had constructed two redoubts and additional fortifications and ordered Danish farmers to create a moat by tearing up the ice close to the shore. A strong current was discovered at the shore, creating a broken ice channel. The Danes spotted the Swedish force and bombarded it with their cannon. On the evening of 29 January, quartermaster general Erik Dahlbergh was dispatched to test the ice on the narrowest strait at Middelfart. During a nighttime observation, he found the ice sufficiently thick for an entire army to cross and raced back to the king with his report. But Charles X Gustav had already decided the army would cross the ice towards Iversnæs, ordering his troops to prepare to march the following morning. During the night, he dispatched troops to build bridges with boards and straw across weaker ice sections and gaps beyond Brandsø. Reconnaissance patrols were sent both north and south of Iversnæs to take measurements of the current. The Swedes planned to cross the ice in a relatively scattered formation, to minimize the risk of the ice breaking under them. This created a dilemma as the Danes on Funen could locate and strike the approaching Swedish isolated units quickly.
Order of battle
Swedish army
On the morning of Saturday, 30 January, Charles X Gustav moved out with his army to Brandsø. Then the army was lined up on the ice. According to one source his troops numbered between 6,000 and 7,000 men, according to others up to 12,000 men. The cavalry was grouped into two wings. Carl Gustaf Wrangel, together with Lieutenant General Clas Tott, led the right wing of 1,500 men, while the left wing with 2,300 men was under the king's command. But as the king moved back and forth between the units, Major General Fabian Berendes held the direct command of the left wing. The infantry, under the command of Lieutenant General Jakob Kasimir De la Gardie, advanced behind the cavalry and took a different and longer route across the ice, carrying both the artillery and baggage train. As a result, they were unable to take part in the battle against the Danes. All units planned to converge at Tybrind Vig north of Iversnæs, approximately 5 kilometres (3.1 mi) from Brandsø.
More than 40 Swedish regiments were to advance towards Funen. Due to battle casualties and disease, the strength of some regiments had fallen to a few dozen men, while others amounted to 500 men or more. The Drabant Corps, the king's elite guards, marched at the head of the cavalry. The cavalry consisted of the Småland, Uppland, Västergötland and Östergötland cavalry regiments. From Finland came Fabian Berendes' dragoons from Åboland, Henrik Horn's cavalry from Tavastia, and cavalry from Turku and Pori Province under the command of Colonel Gustaf Kurck. The infantry consisted of the Hälsinge, Kalmar, Kronoberg, Närke-Värmland, Skaraborg, Södermanland and Uppland regiments. They were spearheaded by the Life Guards, where Swedish guardsmen were mixed with several hundred enlisted German soldiers, who filled the ranks of the regiment severely depleted by plague whilst garrisoned in the Polish city of Thorn.