The Grebbe Line was a forward defence line of the Dutch Water Line, based on inundation. The Grebbe Line ran from the Grebbeberg in Rhenen northwards until the IJsselmeer.

The Dutch Waterline was a series of water-based defences conceived by Maurice of Nassau in the early 17th century, and realised by his half brother Frederick Henry. Combined with natural bodies of water, the Waterline could be used to transform Holland, the westernmost region of the Netherlands and adjacent to the North Sea, almost into an island. In the 19th century, the Line was extended to include Utrecht.