Kūlgrinda

Manmade submerged ford across swamps, found in and around Lithuania

Kūlgrinda is a hidden, usually winding, underwater stony road or ford across swamps, swampy areas, lakes, or along rivers, used as a defense in the lands of Baltic tribes, in particular, in the history of Lithuania. Similar secret roads made primarily of wood and ground were known as medgrinda and žemgrinda respectively. Old Prussians are known to build kulgrindas already in the first centuries, while the Lithuanian ones are dated to the Middle Ages.

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