The Vikram era, or Vikram samvat is an Indian calendar starting in 57 BC. The date is supposed to show when the King Vikramaditya beat the Sakas, who had invaded Ujjain. A new calendar was started just to honor this time.
The story of this event is told by a monk called Mahesara Suri.
The powerful king of Ujjain, called Gardabhilla, kidnapped a nun, who was the sister of the monk. The monk went to the Saka King to get help, and in the end, the Saka King beat Gardabhilla and catpured him and made him a prisoner. But in the end, Gardabhilla was forgiven and run away to a forest, where he was killed by a tiger.
Later on Vikramaditya invaded Ujjain and drove away the Sakas. To commemorate this event he started a new era called the Vikrama era.