Kärnan is a medieval tower, the only part remaining of a larger Danish fortress which controlled the entrance to the Baltic Sea.
The origins of the fortress is disputed but Danish legend places its origin to the reign of the legendary King Fróði. However, this legend has not been supported by archaeological proof. Dendrochronological dating has shown that the core was built in the 1310s, when Eric VI of Denmark was King of Denmark. It was considered the most important fortress in Denmark, and was integral in securing control over the strait between Scania and Zealand.
It was surrendered to Sweden along with the rest of Skåneland as part of the Treaty of Roskilde in 1658. The fortress was retaken by Danish forces in 1676 during the Scanian War, and its capture celebrated by flying a giant Flag of Denmark above it. This flag was later captured by the Swedish army and is preserved in the Army Museum (Armémuseum) in Stockholm. The fortress returned to Swedish control by the Treaty of Lund in 1679. Charles XI of Sweden ordered most of it demolished fearing that it was too exposed to a sneak attack from Denmark. The only thing that was saved for posterity was the old medieval tower core. The tower continued to serve as a landmark for shipping through Øresund.
The castle was restored starting during 1893-94, under instructions from Oscar Ferdinand Trapp, a Swedish businessman and engineer (1847–1916). Architect for the restoration was Josef Alfred Hellerström (1863–1931), Helsingborg city architect from 1903 to 1928. The objective of the restoration was to restore, to the extent possible, the appearance the structure had based upon the oldest known medieval illustration. The building's crenellation dates from these repairs.
References:House of the Blackheads (Melngalvju nams) is a building situated in the old town of Riga. The original building was erected during the first third of the 14th century for the Brotherhood of Blackheads, a guild for unmarried German merchants in Riga. Major works were done in the years 1580 and 1886, adding most of the ornaments.
The structure was bombed to a ruin by the Germans June 28, 1941 and the remains demolished by the Soviets in 1948. The current reconstruction was erected from 1995 to 1999. Today the House of Blackheads serves as a museum and sometimes concert hall.