He reigned 1167–1195 and had fortresses built on the Swedish east coast as defence against enemies from the other side of the Baltic Sea.

The fortress was damaged on a number of occasions during these centuries, including in 1361, when King Valdemar IV (Atterdag) of Denmark attacked Borgholm.

[2] During the Kalmar Union, many castles and fortresses in Sweden were damaged as a result of the ongoing conflicts between Danes and Swedes.

When Gustav Eriksson became Swedish king and the union was dissolved, he, together with the sons that followed him on the throne, invested huge sums of money in repairing these buildings.

[3] During his reign, the Pahr brothers (four engineers and architects from Milan) led a significant rebuilding that took place from 1572.

In the summer of 1989, Swedish pop group Roxette shot material for six music videos during a concert.