King Erik was then on the throne of Sweden, but Birger, the son of a great earl of Gothland, became a famous warrior, and as the king had no sons he made Birger a jarl, or earl, and chose him as his heir. One of the exploits by which Birger had won fame was the following. The town of Luebeck, in North Germany, was closely besieged by the king of Denmark, who had cut it off from the sea by stretching strong iron chains across the river Trave, on which the town is situated. He thus hoped to starve the people into surrender, and would have done so had not Birger come to their rescue. He had the keels of some large ships plated with iron, loaded them with provisions, and sailed up the river towards the beleaguered city. Hoisting all sail before a strong wind, he steered squarely on to the great chains, and struck them with so mighty a force that they snapped asunder and the ships reached the town with their supplies, whereupon the Danish king abandoned the siege. This story is of interest, as these are the first iron-plated ships spoken of in history. By this and other exploits Birger grew in esteem, and when the Finns began their terrible work in the north he and the king summoned the people to arms, and the old warlike spirit, which had long been at rest, was reawakened in the hearts of the Swedes. The Pope at Rome had proclaimed a crusade against the Finns, promising the same privileges to all who took part in it as were enjoyed by those then taking part in the crusades to the Holy Land, and on all sides the people grew eager to engage in this sacred war. Then there was brushing and furbishing on all sides; ancestral swords, which had long hung rusting on the walls, were taken down and sharpened anew; helmets and cuirasses were burnished until they shone like silver or gold; tight-closed purses were opened by those who wished to aid the cause of Christ; and old ships were made ready for the waves and new ones launched. Rosy lips were kissed by lovers who would never kiss them again, and loud was the weeping of the maidens and mothers who saw those they loved setting out for the war, but they consoled themselves as best they could by the thought that it was all for the glory of God. Men of Sweden had gone to the crusades in Palestine, but here was a crusade of their own at home, and all were eager to take part in it. A great fleet was got together and set sail under the command of Birger Jarl. Its course lay up the Gulf of Bothnia, and where it came to land Birger erected a great wooden cross as a sign that he had come for the spread of the Christian faith. From this the place was called Korsholm.