Björn Járnsíða or Björn Järnsida, Swedish king (ca 785-800) was a legendary viking from the 8th century. He was one of the sons of Ragnar Lodbrok. He pillaged in Italy and took part in the conquest of Paris with his father Ragnar Lodbrok.

He acquired the name ironside because he was never wounded in battle. This invulnerability was attributed to his mother Aslaug's use of seid in order to make him impervious to iron and steel.

According to Hervarar saga he inherited Sweden from his father while his brother Sigurd Snake-Eye inherited the remainder of Scandinavia.

The dynasty he founded is called the House of Munsö by modern historians, because a local tradition claims that he is buried in Björnshögen at Husby on the island of Munsö. Many of his dynasty were to be named Björn.

He had two sons, Refil and Erik Björnsson, and Erik succeeded him on the throne.

See also

• Early Swedish Kingdoms
• House of Munsö