The Grebbe Line (Dutch: Grebbelinie) was a Dutch defence line that stretched from the Grebbeberg in Rhenen to the Zuiderzee (present IJsselmeer). The line was based on inundation. Large areas could be flooded if an enemy invasion was imminent. The line was established in 1745 but was never used. In 1815, the construction of the New Dutch Water Line started. The Grebbe Line wasn’t needed anymore and was decommissioned in 1926.
International tensions grew in the late 1930s and the Dutch army prepared for an enemy invasion. In 1940 the decision was made to make the Grebbe Line the main defensive line again. The old fortifications were extended with trenches, roadblocks and casemates.
On May 10, 1940 the German army invaded The Netherlands. Different parts of the Grebbe Line were attacked but the most dramatic fighting took place on the Grebbeberg. The German troops broke through the line on May 13. The Dutch army retreated behind the New Dutch Water Line but surrendered after the bombing of Rotterdam.