Amoat is a deep, broad ditch dug around acastle,fortification,building, or town, historically to provide it with a preliminary line ofdefence. Moats can be dry or filled with water. In some places, moats evolved into more extensive water defences, including natural or artificial lakes,dams andsluices. In older fortifications, such ashillforts, they are usually referred to simply asditches, although the function is similar. In later periods, moats or water defences may be largely ornamental. They could also act as a sewer.
Some of the earliest evidence of moats has been uncovered aroundancient Egyptian fortresses. One example is atBuhen, a settlement excavated inNubia. Other evidence of ancient moats is found in the ruins of Babylon, and in reliefs from ancient Egypt,Assyria, and other cultures in the region.[1][2]
Evidence of early moats around settlements has been discovered in many archaeological sites throughout Southeast Asia, including Noen U-Loke, Ban Non Khrua Chut, Ban Makham Thae and Ban Non Wat. The use of the moats could have been either for defensive or agriculture purposes.[3]
Moats were excavated aroundcastles and other fortifications as part of the defensive system as an obstacle immediately outside thewalls. In suitable locations, they might be filled with water. A moat made access to the walls difficult for siege weapons such assiege towers andbattering rams, which needed to be brought up against a wall to be effective. A water-filled moat made the practice ofmining – digging tunnels under the castles in order to effect a collapse of the defences – very difficult as well.Segmented moats have one dry section and one section filled with water. Dry moats that cut across the narrow part of a spur or peninsula are calledneck ditches. Moats separating different elements of a castle, such as the inner and outer wards, arecross ditches.[citation needed]
The 17th-century fortified town ofNaarden,Netherlands, showing bastions projecting into the wet moat
With the introduction of siegeartillery, a new style of fortification emerged in the 16th century using low walls and projecting strong points calledbastions, which was known as thetrace italienne. The walls were further protected from infantry attack by wet or dry moats, sometimes in elaborate systems.[5] When this style of fortification was superseded by lines ofpolygonal forts in the mid-19th century, moats continued to be used for close protection.[6]
TheWalls of Benin were a combination of ramparts and moats, called Iya, used as a defence of the capitalBenin City in present-day Edo State of Nigeria. It was considered the largest man-made structure lengthwise, second only to theGreat Wall of China and the largest earthwork in the world. Recent work by Patrick Darling has established it as the largest man-made structure in the world, larger thanSungbo's Eredo, also in Nigeria. It enclosed 6,500 km2 (2,500 sq mi) of community lands. Its length was over 16,000 km (9,900 mi) of earth boundaries. It was estimated that earliest construction began in 800 and continued into the mid-15th century.[citation needed]
The walls are built of a ditch and dike structure, the ditch dug to form an inner moat with the excavated earth used to form the exterior rampart.[citation needed]
The Benin Walls were ravaged by the British in 1897. Scattered pieces of the walls remain in Edo, with material being used by the locals for building purposes. The walls continue to be torn down for real-estate developments.[citation needed]
The Walls of Benin City were the world's largest man-made structure.Fred Pearce wrote inNew Scientist:
They extend for some 16,000 kilometres in all, in a mosaic of more than 500 interconnected settlement boundaries. They cover 6,500 square kilometres and were all dug by the Edo people. In all, they are four times longer than the Great Wall of China, and consumed a hundred times more material than the Great Pyramid of Cheops. They took an estimated 150 million hours of digging to construct, and are perhaps the largest single archaeological phenomenon on the planet.[7]
Map of theTokyo Imperial Palace and surrounding Gardens showing the elaborate moat system
Japanese castles often have very elaborate moats, with up to three moats laid out in concentric circles around the castle and a host of different patterns engineered around the landscape. The outer moat of a Japanese castle typically protects other support buildings in addition to the castle.[citation needed]
As many Japanese castles have historically been a very central part of their cities, the moats have provided a vital waterway to the city. Even in modern times the moat system of theTokyo Imperial Palace consists of a very active body of water, hosting everything from rental boats and fishing ponds to restaurants.[8]
Most modern Japanese castles have moats filled with water, but castles in the feudal period more commonly had 'dry moats'karabori (空堀,lit.'empty moat'), atrench. Atatebori (竪堀,lit.'vertical moat') is a dry moat dug into a slope. Aunejo tatebori (畝状竪堀,lit.'furrowed shape empty moat') is a series of parallel trenches running up the sides of the excavated mountain, and the earthen wall, which was also calleddoi (土居,lit.'earth mount'), was an outer wall made of earth dug out from a moat. Even today it is common for mountain Japanese castles to have dry moats. Amizubori (水堀,lit.'water moat') is a moat filled with water.[citation needed]
The only moated fort ever built in Australia wasFort Lytton inBrisbane. As Brisbane was much more vulnerable to attack than either Sydney or Melbourne a series of coastal defences was built throughoutMoreton Bay, Fort Lytton being the largest. Built between 1880 and 1881 in response to fear of a Russian invasion, it is a pentagonal fortress concealed behind grassy embankments and surrounded by a water-filled moat.[citation needed]
TheMaya people also used moats, for example in the city ofBecan.
European colonists in the Americas often built dry ditches surrounding forts built to protect important landmarks, harbours or cities (e.g.Fort Jay onGovernors Island inNew York Harbor).
Whilst moats are no longer a significant tool of warfare, modern architectural building design continues to use them as a defence against certain modern threats, such as terrorist attacks fromcar bombs andimprovised fighting vehicles. For example, the new location of theEmbassy of the United States in London, opened in 2018, includes a moat among its security features - the first moat built in England for more than a century.[9] Modern moats may also be used for aesthetic or ergonomic purposes.
Moats, rather than fences, separate animals from spectators in many modernzoo installations. Moats were first used in this way byCarl Hagenbeck at hisTierpark inHamburg, Germany.[11] The structure, with a vertical outer retaining wall rising direct from the moat, is an extended usage of theha-ha of English landscape gardening.[citation needed]
In 2004, plans were suggested for a two-mile moat across the southern border of theGaza Strip to prevent tunnelling from Egyptian territory to the border town ofRafah.[12]
In 2008, city officials inYuma, Arizona planned to dig out a two-mile stretch of a 180-hectare (440-acre) wetland known as Hunters Hole to control immigrants coming from Mexico.[13]
Researchers ofjumping spiders, which have excellent vision and adaptable tactics,[14] built water-filled miniature moats, too wide for the spiders to jump across. Some specimens were rewarded for jumping then swimming and others for swimming only.Portia fimbriata fromQueensland generally succeeded, for whichever method they were rewarded.[15] When specimens from two different populations ofPortia labiata were set the same task, members of one population determined which method earned them a reward, whilst members of the other continued to use whichever method they tried first and did not try to adapt.[16]
As a basic method of pest control inbonsai, a moat may be used to restrict access of crawling insects to the bonsai.[citation needed]
^Jackson, Robert R.; Chris M. Carter; Michael S. Tarsitano (2001). "Trial-and-error solving of a confinement problem by a jumping spider,Portia fimbriata".Behaviour.138 (10). Leiden: Koninklijke Brill:1215–1234.doi:10.1163/15685390152822184.ISSN0005-7959.JSTOR4535886.
