Located near the site of Kalmar's medieval harbor, it has played a crucial part in Swedish history since its initial construction as a fortified tower in the 12th century.

During the Swedish rebellion against Denmark in 1520, the fortress was commanded by Anna Eriksdotter (Bielke), who at the death of her spouse, Johan Månsson Natt och Dag, in the middle of the rebellion, took control over his fiefs and defended Kalmar against Denmark.

The three commanders were subsequently killed, along with nineteen other members of the garrison, in a mass execution traditionally known as the Second Kalmar Bloodbath.

Repairs were begun, but from the end of the seventeenth century the castle was allowed to fall into disrepair.

In 1919 Professor Martin Olsson was charged with the continuing restoration of earthworks, the moat, the bridge and the drawbridge.