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A causeway is a track, road or railway on the upper point of an embankment across "a low, or wet place, or piece of water". It can be constructed of earth, masonry, wood, or concrete. One of the earliest known wooden causeways is the Sweet Track in the Somerset Levels, England, which dates from the Neolithic age. (1992). 9780948578380, Ex Libris Press. ISBN 9780948578380 Timber trackway may also be described as both and .
Originally, the construction of a causeway used earth that had been trodden upon to compact and harden it as much as possible, one layer at a time, often by slaves or flocks of sheep. Today, this work is done by machines. The same technique would have been used for road embankments, raised river banks, sea banks and fortification earthworks.
The second derivation route is simply the hard, trodden surface of a path. The name by this route came to be applied to any firmly surfaced road. It is now little-used except in dialect and in the names of roads which were originally notable for their solidly made surface. The 1911 Encyclopædia Britannica states: "causey, a mound or dam, which is derived, through the Norman-French caucie (cf. modern chaussée), from the late Latin via calciata, a road stamped firm with the feet (calcare, to tread)."
The word is comparable in both meanings with the French language , from a form of which it reached English language by way of Norman language. The French adjective chaussée carries the meaning of having been given a hardened surface and is used to mean either paved or shod. As a noun chaussée is used on the one hand for a metalled carriageway, and on the other for an embankment with or without a road.
Other languages have a noun with similar dual meaning. In Welsh language, it is sarn. The Welsh is relevant here, as it also has a verb sarnu, meaning to trample. The trampling and ramming technique for consolidating earthworks was used in fortifications and there is a comparable, outmoded form of wall construction technique, used in such work and known as pisé, a word derived not from trampling but from ramming or tamping. The Welsh word cawsai translates directly to the English word 'causeway'; it is possible that, with Welsh being a lineal linguistic descendant of the original native British tongues, the English word derives from the Welsh.
A transport corridor that is carried instead on a series of arches, perhaps approaching a bridge, is a viaduct; a short stretch of viaduct is called an overpass. The distinction between the terms causeway and viaduct becomes blurred when flood-relief are incorporated, though generally a causeway refers to a roadway supported mostly by earth or stone, while a bridge supports a roadway between piers (which may be embedded in embankments). Some low causeways across shore waters become inaccessible when covered at high tide.
In East Africa, the Husuni Kubwa (the "Great Fort"), situated outside the town of Kilwa Kisiwani, was an early 14th-century sultan's palace and emporium that featured causeways made from blocks of reef and coral nearly a meter high. These acted as breakwaters, allowing mangroves to grow which is one of the ways the breakwater can be spotted from a distance. Some parts of the causeway are made from the bedrock, but usually the bedrock was used as a base. Coral stone was also used to build up the causeways, with sand and lime being used to cement the cobbles together. However, some of the stones were left loose.
In Scotland, the skirmish known as Clense the Calsey, or Cleanse the Causeway, took place in the Royal Mile in 1520.
In the 18th century, Dahomey lacked an effective navy hence it built causeways for naval warfare starting in 1774.
Causeways are also common in Florida, where low bridges may connect several human-made , often with a much higher bridge (or part of a single bridge) in the middle so that taller may pass underneath safely. Causeways are most often used to connect the with the mainland. In the case of the Courtney Campbell Causeway, however, the mainland (Hillsborough County) is connected by a causeway to a peninsula (Pinellas County). A well-known causeway is the NASA Causeway connecting the town of Titusville on the Florida mainland to the rocket-launching facility at the Kennedy Space Center on Merritt Island.
The Churchill Barriers in Orkney are some of the most notable sets of causeways in Europe. Constructed in waters up to 18 metres deep, the four barriers link five islands on the eastern side of the natural harbour at Scapa Flow. They were built during World War II as military defences for the harbour, on the orders of Winston Churchill.
The Estrada do Istmo connecting the islands of Taipa and Coloane in Macau was initially built as a causeway. The sea on both sides of the causeway then became shallower as a result of silting, and mangroves began to conquer the area. Later, land reclamation took place on both sides of the road and the area has subsequently been named Cotai and become home to several casino complexes.
Causeways can separate populations of wildlife, putting further pressure on endangered species.
Causeways can cause a mineral imbalance between portions of a body of water. For example, the Lucin Cutoff, built across the Great Salt Lake has caused the northern half of the lake to have much higher salinity, to the point that the two halves show a major color imbalance. Furthermore, the difference in salinity has become so severe that native brine shrimp cannot survive in much of the waters, with the northern part being too salty and the southern part being insufficiently salty.
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