The area around Kalmar has been inhabited since ancient times. Diggings have found traces of stone age gravefields. The oldest sources of there being a town are however from the 11th century. According to a medieval folk tale, the Norwegian patron Saint Olav had his ships moved to Kalmar. The oldest city seal of Kalmar is from somewhere between 1255�1267, making it the oldest known city seal in Scandinavia.
In the 12th century the first foundations of a castle were established, with the construction of a round tower for guard and lookout. The tower was continuously expanded on in 13th century, and as such, Queen Margaret called an assembly there between head of states of Sweden and Norway, and on July 13, 1397, the Kalmar Union treaty was signed, which would last until 1523. Kalmar's strategic location, near the Danish border (at the time the Scanian lands, i.e. the provinces of Blekinge, Halland and Scania, were part of Denmark), and its harbour and merchancy, also involved it into several feuds. There are two events independently labelled Kalmar bloodbath: The first in 1505, when King John of Denmark, Norway, and Sweden let execute the mayor and city council of Kalmar; the second in 1599 by command of Duke Charles, later to became King Charles IX of Sweden.
In the 1540s, first King Gustav Vasa, and later his sons Erik XIV of Sweden and John III of Sweden would organize a rebuilding of the castle into the magnificent Renaissance castle it is today.
Kalmar became a diocese in 1602, a position it held until 1903. In 1634, Kalmar County was founded, with Kalmar as the natural capital. In 1660, the Kalmar Cathedral was begun by drawings of Nicodemus Tessin the Elder. It would be inaugurated in 1703.
In 1611-1613, it suffered in the Kalmar War, which began with a Danish siege of Kalmar Castle. 1611 is mentioned as the darkest year of Kalmar's history, but by no means the only dark year; much blood has been shed in the vicinity of the castle
