During the revolutionary ferment of 1848-49 he urged the Prussian king to refuse the imperial crown, co-operated with the Austrian emperor in suppressing the Hungarian insurrection, and compelled the Prussians to withdraw their support from the insurgents in Schleswig-Holstein.
It passed in 1559 to Duke John the Younger, founder of the line of Holstein-Sonderburg, on the extinction of which, in 1761, it fell to Denmark, and in 1867, with Schleswig-Holstein, to Prussia.
Forchhammer was a democrat in the best sense of the word, and from 1871 to 1873 represented the progressive party of Schleswig-Holstein in the German Reichstag.
The church of St Peter, erected about 1too and renewed in the Gothic style in the 15th century, has a lofty steeple (365 ft.) and contains a very fine carved oak reredos by Hans Bruggemann, which is regarded as the most valuable work of art in Schleswig-Holstein.
At the partition of 1544 the old château of Gottorp, originally built in 1160 for the bishop, became the residence of the Gottorp line of the Schleswig-Holstein family, which remained here till expelled by the Danish king Frederick IV.