From the start the Wendish Crusade suffered from divided leadership and while the German contingent enjoyed modest success, the Danes were defeated. It was not until 1159 that the Danes finally enjoyed a major victory, when the young Valdemar the Great (r. 1157 – 82) flexed his military muscles and led a successful Viking-style raid on the Wendish island of Rügen. Valdemar’s success convinced the powerful Saxon duke Henry the Lion that he would make a useful ally in combined operations against the Wends, with the Saxons attacking them by land and the Danes attacking from the sea. After joint victories in 1160 and 1164, the alliance fell apart as the two rulers quarrelled over the spoils and thereafter regarded each other as rivals. But by this time Valdemar no longer needed Henry’s support. Valdemar’s tactics against the Wends were an almost seamless continuation of those used by the Vikings. Raiding parties made surprise landings from fleets of longships, sweeping quickly inland to plunder and return to their ships before the Wends could organise resistance. One departure from Viking traditions was that each longship carried four horses so that armoured knights could join the raids. Although they could not take the strongly fortified Wendish towns, the Danes brought them to their knees through economic warfare, burning crops and villages, taking livestock and captives, and by preying on Wendish merchant shipping. These tactics had the great advantage of being very profitable. Wendish retaliation was blunted by constructing castles at strategic locations on the Danish coast and by mounting naval patrols to look out for approaching pirate fleets. In most of his campaigns, Valdemar was accompanied by Absalon, the warlike bishop of Roskilde, who is best known today as the founder of Copenhagen. Absalon took great pleasure in destroying the idols of the Wendish gods to demonstrate their powerlessness, but religion was a secondary concern for Valdemar: his main aims were to seize plunder and territory, and end Wendish pirate raids on Denmark.
Decisive success came in 1168, when Valdemar plundered and burned the cliff-top sanctuary of the Wendish high-god Svantovit at Arkona on Rügen. The shocked Rugians surrendered, accepted Danish rule and submitted to baptism. Now joined by the Rugian fleet, the Danes destroyed the Liutizian pirate stronghold of Dziwnów on the island of Wolin near the mouth of the Oder in 1170, so removing another threat to their security. After the Danes defeated a Wendish pirate fleet in a sea battle off the island of Falster two years later, Wendish pirates never ventured into Danish waters again. By 1185 the Danish tactic of devastating Viking-style raids had forced the submission of the Liutizians and the Pomeranians to give them control of the entire Baltic Sea coast from Rügen east to the mouth of the River Vistula. Conquest was not followed by military occupation or settlement, however. The Wends simply became tributaries of the Danes, who counted on the threat of punitive raids to keep their vassals loyal.
Crusading in the Baltic region received a new impetus in 1193, when pope Celestine III called for a crusade against the Livonians, a group of tribes who lived in what is now Latvia and Estonia. The papacy’s motive in this crusade was not simply the conversion of pagans, it was also to prevent the area coming under the influence of what it saw as the heretical Orthodox church. The Livonian Crusade was dominated from the outset by German crusading orders such as the Livonian Knights, the Sword Brothers and the Teutonic Knights, but the Danish king Valdemar II (r. 1202 – 41) saw an opportunity for territorial expansion and in 1218 he won full papal blessing for an invasion of Estonia. Valdemar landed at the Estonian trading place of Lyndanisse (modern Tallinn) in June the next year with a fleet of 500 longships. Longships were becoming decidedly old-fashioned by this time and this was probably the last occasion that they were used on such a large scale in the Baltic. Apart from the adoption of the stern-post rudder in place of the less-effective side rudder, longships had changed little since the Viking Age and they had long exhausted their development potential. German crusaders were now sailing the Baltic in cogs, a type of ship that probably originated in Frisia in the Viking Age. Unlike longships, cogs had no oars and relied entirely on a single square sail. Though they could not compete with longships for speed and manoeuvrability, cogs were sturdy and seaworthy, with broad, deep hulls and high sides, and were cheaper and easier to build. Cogs were first built to carry bulky cargoes – even the smallest cogs could carry twice the 20-ton cargo of a Viking knarr – but they proved surprisingly well-suited to war. Especially when fitted with wooden fighting platforms at the bows and stern, cogs towered over longships, giving their crews a clear advantage in a sea battle. Scandinavian technological conservatism helped the German-dominated Hanseatic League of mercantile cities – early adopters of the cog – to supplant the Scandinavians as the main trading and naval power in the Baltic in the course of the thirteenth and fourteenth centuries. Scandinavians continued to build longships for the coastal defence levy fleets until the early fifteenth century, but their ineffectiveness in battle against cogs had been demonstrated many times by then.
It is thought that Valdemar set up camp on the Toompea, a steep-sided flat-topped hill rising around 100 feet (30.5 m) above the harbour at Tallinn, giving excellent views over the sea and low lying coastlands. As well as being a good defensive position, the hill had religious significance to the Estonians, who believed that it was the burial mound of their mythological hero Kalev. Apparently overawed by the strength of Valdemar’s fleet, the Estonian chiefs agreed to submit and a few even allowed themselves to be baptised. However, this was all a ruse to lull the Danes into a false sense of security and the Estonians achieved complete surprise when they attacked the Danish camp a few days later. The battle of Lyndanisse achieved legendary stature in Danish historical traditions as the place where the country’s national flag, the Dannebrog, fell from Heaven as a sign to encourage the embattled Danes to fight on and overcome the pagans. Some historians have tried to rationalise this story, explaining it away as the sighting of an unusual weather phenomenon, but it is more likely to be pure fiction. The legend cannot be traced back any earlier than the sixteenth century, and the earliest known the use of the Dannebrog dates only to 1397, nearly 200 years after the battle. After his victory, Valdemar built a castle on the Toompea which, despite being incomplete, held out against an Estonian siege in 1223. It is from Valdemar’s castle that Tallinn’s name is derived, from Taani-linn, meaning the ‘Danes’ castle’: rebuilt many times, it now houses the Estonian parliament. After Valdemar’s final victory over the Estonians in 1224, a stone cathedral was built near the castle and the Toompea became the main centre of Danish secular and ecclesiastical government in Estonia. Tallinn has the best harbour on the Estonian coast and it soon attracted German merchants, who settled on the lower ground between the Toompea and the harbour, creating a commercial Lower Town. In 1285 the city, known to the Germans as Reval, joined the Hanseatic League and Germans continued to dominate the city’s economy until the twentieth century. Outside Tallinn, most of the land was parcelled out not to Danes but to Saxon lords, who paid a land tax to the Danish crown.