From there his armies marched across the frozen sea to threaten Copenhagen; the subsequent Treaty of Roskilde (1658) broke Denmark and gave the Swedish empire its widest territorial extent. However, the long regency of his son and heir, Karl XI, did little to enhance Sweden's vulnerable position, so extensive were its borders. On his assumption of power in 1672 Karl was almost immediately dragged into war; beaten by a smaller Prussian army at Brandenberg in 1675, Sweden was suddenly faced with war against both the Danes and Dutch. Karl rallied, though, to drive out the Danish invaders, the war ending in 1679 with the reconquest of SkSne and the restoration of most of Sweden's German provinces. In 1682 Karl XI became absolute monarch and was given full control over legislation and reduktion the resumption of estates previously alienated by the crown to the nobility. The armed forces were reorganised too and by 1700 the Swedish army had 25,000 soldiers and twelve regiments of cavalry; the naval fleet was expanded to 38 ships and a new base built at Karlskrona (nearer than Stockholm to the likely trouble spots). Culturally, Sweden began to benefit from the innovations of Gustavus Adolfus. Gemms (grammar schools) continued to expand and a second university was established at Lund in 1668 A national literature emerged, helped by the efforts of George Stiernhielm, "father"' of modem Swedish poetry. Olof Rudbeck (16301702) was a Nordic polymath whose scientific reputation lasted longer than his attempt to identifv the ancient Goth settlement at Uppsala as Atiantis Architecturally, this was the age of Tessin both father and son. Tessin the Elder was responsible for the glorious palace at Drottningholm. work on which began in 1662, as well as the cathedral at Kalmar. His son, Tessin the Younger, succeeded him as royal architect and was to create the new royal palace at Stockholm. In 1697 the fifteenyearold Karl XII succeeded to the throne and under him the empire collapsed. Faced with a defensive alliance of Saxony, Denmark and Russia, there was little the king could have done to avoid eventual defeat. However, he remains a revered figure for his valiant (often suicidal) efforts to prove Europe wrong. Initial victories against Peter the Great and Saxony led him to march on Russia, where he was defeated and the bulk of his army destroyed. Escaping to Turkey, where he remained as guest and then prisoner for four years, Karl watched the empire disintegrate. With Poland reconquered by Augustus of Saxony, and Finland by Peter the Great, he returned to Sweden only to have England declare war on him. Eventually, splits in the enemy's alliance led Swedish diplomats to attempt peace talks with Russia. Kari, though, was keen to exploit these differences in a more direct fashion. In order to strike at Denmark, but lacking a fleet, he besieged Fredrikshald in Norway in 1718 and was killed by a sniper's bullet.