During the 13th and 14th century Northern Crusades, pagan Lithuanian and Samogitian defenders built secret underwater stone causeways across peat bogs to move cavalry and carts between fortresses:

Laid below the swamp waterline so they were invisible from the surface, these kūlgrindos deliberately twisted through low-lying mire rather than taking the shortest crossing—as archaeologist Ludwik Krzywicki found in 1903 when surveying 3 surviving stone stretches (250 m, 180 m, and 150 m) linking the fortresses of Medvėgalis, Paršpilis, and Šiuraičiai at Sietuva—so pursuing Crusaders unfamiliar with the turns would step off the submerged stones into deep bog mud.