Pile barrage
Pile barrages, among other names, are underwater barricades or barrages used for coastal military defence. They are constructed with piles, vertical poles or stakes driven into the bed of a body of water, extending up to, or above, the water line to block the passage of watercraft. They are sometimes also mixed with floating booms and thereof.
They have been used since prehistory to prevent enemy watercraft from entering waterways or harbors, etc., as to protect the sailing routes to trading posts and settlements.
Terminology
The defensive structure lacks an established English name. Various sources either gives it a descriptive name: "pile barrage", "pole barrage", "pole-built barrage", "pile barrier", "underwater barrier", "pole blockage", etc., mainly derrived from ; while others simply use unspecified terms, such as "barrage" or "barrier".A descriptive term could potentially be "staked or piled waterway", based on Old Norse nomenclature: "stikudu Gautar Gautelfi".
The Old Norse name for the structure was an ablaut-form cognate to "stake" – Old West Norse: stik, stika; Old East Norse: stœk, stækh; surviving as, dialectally: stege, Norwegian, stike,, steg, stig, stag, dialectally: stika, stiku; variously meaning pole, stake etc., including strait, and archaicly pile barrage etc.
Description
Use
As a defensive measure, pile barrages allows the defender to control the engagement of enemy coastal attacks; by hindering armadas from entering and landing where they want, the landing party can be forced to step ashore further away from the target than intended, giving time for the defender to prepare defenses, and forcing the enemy to travel by land, wasting them time and energy; potentially, blocking the enemy armada far away enough to were it is forced to cancel the invasion by practicality; alternatively, the enemy armada can be forced into passages where the defender can perform controlled ambushes.As a civilian measure, pile barrages have also been used to block a waterway as a kind of customs fence, with the aim of forcing ships with dutiable goods past a customs station. An example of this is Pålsundet in Stockholm, dating back to the time of Gustavus Adolphus. It was introduced in 1622 as a toll station for traffic to and from the lake Mälaren and the strait was staked to stop evaders.
Construction
Pile barrages can be tens of meters in depth; the piles, usually full length tree trunks, being driven down at down at least a third below the bottom, to resist ship hits, and outfitted with barbs carved into them, as to prevent foes from pulling them up and escaping through.Northern Europe
Pile barrages were common in Northern Europe during the Iron Age into the Medieval Period, especially in Norse Scandinavia, still found in many placenames related to waterways in Sweden: Almarestäket, Baggensstäket, Stegeborg, Stocksundet, Pålsundet, among many others.Iron Age
According to the Old Norse-Icelandic rendering of Historia Regum Britanniae: Breta sögur, the Britons had stakes, armored with lead and iron, driven into the river Thames, in order to protect themselves from the Roman fleet: "hann let stik gera i ana Temps".Viking Age
pile barrages are described various times in the written corpus. In Snorri Sturlason's Heimskringla, it is told how Harald Fairhair, around 870–900, who had recently succeeded in uniting Norway, intended to expand his empire with attacks in the Göta river. In the spring when the ice broke up, the Geats "staked" the Göta river so that the king would not be able to bring his ships up the country: "stikudu Gautar Gautelfi". He then steered his ships up the River and docked at "stikin", ravaged both banks and burned the countryside. In Saint Olaf's Saga, "stik" is mentioned regarding defensive measures in the unidentified lake "Lagen" in Sweden. The Danish historian Saxo Grammaticus mentions that, in the 1150s, the Danes blocked bays and fjords with long piles against the Slavic pirate ships. Baggensstäket in the Stockholm archipelago is named the "Harustik" in the Danish Census Book's itinerarium from 1231. Stegeborg is first mentioned in 1290–1296 as "castrum Stakæburgh" and in 1310 as "Stækaborg".Several Viking Age pile barrages have been found and excavated. On the seabed in the strait between western Skällö and eastern Skällö, the remains of a 290 meter long prehistoric Viking Age pile barrage has been found. It blocked the strait and forced ships to take a detour past neighbouring Skällenäs. The piles, which are made of oak, beech and birch, have been driven into the bottom. Such were examined by Blekinge Museum in 2023 and dated to around 1050.
Middle Ages
A famous Nordic pile barrage was the Medieval "city pile wall" of Stockholm, during the Middle Ages, simply called "the boom". Like the city gate, the boom could be opened and locked. The opening parts were of a floating raft construction made of linked logs. The barrier had several entrance openings that were closed with bars at night and in case of danger. The structure functioned both as a customs fence and a boundary for the inner port area.File:Pålkran 1500-tal.jpg|thumb|The Stockholm pile driver operating on ice, from Olaus Magnus' A Description of the Northern Peoples.
Due to erosion, the piles had to be replaced regularly. During the early 16th century, several hundred poles were purchased that were 24 meters long and more, due to the delpth in certain locations. Later, it was difficult to obtain such long logs and people began to join logs using nails and forged joint rings. A special pile driver was used to drive the piles into the lakebed, which was mounted on the city's barge. In winter, the piles could be driven down from the ice.