The new monarch was a reserved, enigmatical prince, who seldom laughed, spoke little and wrote less--a striking contrast to Christian IV. But if he lacked the brilliant qualities of his impulsive, jovial father, he possessed in a high degree the compensating virtues of moderation, sobriety and self-control. But with all his good qualities Frederick was not the man to take a clear view of the political horizon, or even to recognize his own and his country's limitations. He rightly regarded the accession of Charles X. of Sweden (June 6th, 1654) as a source of danger to Denmark. He felt that temperament and policy would combine to make Charles an aggressive warrior-king: the only uncertainty was in which direction he would turn his arms first. Charles's invasion of Poland (July 1654) came as a distinct relief to the Danes, though even the Polish War was full of latent peril to Denmark. Frederick was resolved upon a rupture with Sweden at the first convenient opportunity. The _Rigsdag_ which assembled on the 23rd of February 1657 willingly granted considerable subsidies for mobilization and other military expenses; on the 15th of April Frederick III. desired, and on the 23rd of April he received, the assent of the majority of the _Rigsraad_ to attack Sweden's German provinces; in the beginning of May the still pending negotiations with that power were broken off, and on the 1st of June Frederick signed the manifesto justifying a war which was never formally declared. The Swedish king traversed all the plans of his enemies by his passage of the frozen Belts, in January and February 1658 (see CHARLES X. of Sweden). The effect of this unheard-of achievement on the Danish government was crushing. Frederick III. at once sued for peace; and, yielding to the persuasions of the English and French ministers, Charles finally agreed to be content with mutilating instead of annihilating the Danish monarchy (treaties of Taastrup, February 18th, and of Roskilde, February 26th, 1658). The conclusion of peace was followed by a remarkable episode. Frederick expressed the desire to make the personal acquaintance of his conqueror; and Charles X. consented to be his guest for three days (March 3-5) at the castle of Fredriksborg. Splendid banquets lasting far into the night, private and intimate conversations between the princes who had only just emerged from a mortal struggle, seemed to point to nothing but peace and friendship in the future. But Charles's insatiable lust for conquest, and his ineradicable suspicion of Denmark, induced him, on the 17th of July, without any reasonable cause, without a declaration of war, in defiance of all international equity, to endeavour to despatch an inconvenient neighbour.