Causantín or Constantín mac Fergusa (English: "Constantine son of Fergus") (before 775–820) was king of the Picts (or of Fortriu), in modern Scotland, from 789 until 820. He was until the Victorian era sometimes counted as Constantine I of Scotland; the title is now generally given to Causantín mac Cináeda. He is credited with having founded the church at Dunkeld which later received relics of St Columba from Iona.