From time immemorial, the Ertholmene archipelago has been important, because the strait between Christiansø and Frederiksø formed a natural harbour – with entrances to both the north and the south making it possible to access the harbour regardless of wind direction.
In the Middle Ages, Ertholmene was a rugged and desolate place, frequented by Wendish pirates who ravaged the Danish waters. Around the year 1080, King Canute sent his earl, Blood Egil the Viking, to Ertholmene with a company of guards to keep the pirates away. The temptation proved too much for Blood Egil, however, who ended up plundering a ship at Ertholmene and burning its crew alive.
In the 1300s, Ertholmene was used as a base by pirates from the Hanseatic lands in Germany, and for this same reason, Queen Margrethe I had plans to build a castle on the islands to keep the pirates at bay.
In periods of peace, the islands’ natural harbour was used by fishermen from Bornholm, who stayed on the islands during the summer months.
In the late 1000s, pirates frequented the Ertholmene archipelago. They used the natural harbour as a base for raids on Bornholm. In 1080, King Canute therefore sent his earl, Blood Egil the Viking, to Bornholm.
Blood Egil took up residence at Ertholmene with a host of soldiers to keep the pirates away. But the temptation proved too much for Blood Egil, as a Norwegian ship disappeared in the Baltic Sea around that same time.
King Canute decided to investigate the case himself and journeyed to the islands. At Ertholmene, he discovered rocky outcrops that were red as the result of an intense fire. The king confronted Blood Egil, who came clean. The Norwegian ship had put into the harbour at Christiansø but became caught by the low tide and was unable to get out. That was when Blood Egil struck, burning the ship with the entire crew on board at the spot where the rocks were red. Blood Egil had to pay with his life for that atrocity.
Fishery before the fortress was built
In 1671, somebody gave the following description of Ertholmene:
‘Here, the good people of Gudhjem have their best trade and fishery and their fish stalls for salting and drying fish and herring in. They sail out as soon as spring arrives, taking with them man and beast, cattle and sheep, feeding them and keeping them on the same islets, which offer plenty of grazing, to ensure milk and subsistence for themselves and their families. Their catches they bring to Copenhagen and other places near by, where they then procure salt, flour, grain and other necessities.
‘A fine example of the practices of old: When fishing in the locality is going well, they light fires and flares in the evening and at night to signal that fishing in these waters is thriving. They are also a nod to their comrades to come and make some coin helping to pull in the fish. And then people from the neighbouring areas arrive in droves, bringing with them bread, beer and other provisions, to provide assistance and take joy together in God’s blessing.’