The Vlie or Vliestroom is the seaway between the Dutch islands of Vlieland, to its northeast, and Terschelling, to its southwest. The Vlie was the estuary of the river IJssel in medieval times. In 1666 the English Admiral Robert Holmes burnt a Dutch merchant fleet of 130 ships (Holmes's Bonfire), that had taken refuge in the Vlie, mistakenly supposing the English could never find their way through the treacherous shoals, so typical for the coastal waters there.