The word was adapted in Middle English from the French motte "mound, hillock" and was first applied to the central mound on which a fortification was erected (see Motte and bailey), and then came to be applied to the excavated ring, a "dry moat". The term moat is also applied to natural formations reminiscent of the artificial structure.
In the violent conditions of the 14th and 15th centuries in England, though defensive walling required a charter from the king, a moat round a manor house could deter all but the most determined intruders (illustration, top right). See also Ightham Mote. Moated fortresses are also evident in Ferrara, the Rocca Sanvitale in Fontanelleta, and the Rocca Scaglieri in Sirmione on the shores of Lake Garda.
Often streams were diverted in the Middle Ages to fill the ditch. Moats required upkeep. They had to be dredged for debris which could potentially form a traversable bridge from one side to another.
Withdrawable bridges spanned moats in the Middle Ages. At first they were only simple wooden bridges that could easily be dismantled if an enemy was about to breach the fortifications. Later Drawbridges were used for moat spans.
Moats sometimes had long wooden spikes in them, to prevent enemies from swimming across. The practice of stocking them with alligators, crocodiles, sharks or other dangerous animals is almost certainly a myth, however.
As late as the seventeenth century, French châteaux that were not remotely fortified nor built on traditionally fortified and moated sites, pleasure houses such as Vaux-le-Vicomte, were surrounded by traditional formal moats that isolated the main corps de logis and were bridged by an axial approach.
Japanese castles often have very elaborate moats, sometimes with many moats laid out in concentric circles around the castle and a host of different patterns engineered around the landscape. Japanese castles will have up to three of these concentric moats. The outer moat typically protects other support buildings in addition to the castle.
As many Japanese Castles have historically been a very central part of their respective city, the moats have respectivially provided a vital waterway to the city. Even in modern times, the moat system of the Japanese Imperial Palace comprises a very active body of water, hosting everything from rental boats and fishing ponds to restaurants..
Most modern Japanese castles have moats filled with water, but castles in the Middle Ages more commonly had 'dry moats' (karahori, 空堀), essentially a trench. Even today, it is common for mountain castles to have dry moats.
Moats were also used in East Asia in the Forbidden City and Xi'an in China and Kokyo Imperial Palace in Japan; in Vellore in India and in Southeast Asia, such as at Angkor Wat in Cambodia and Chiang Mai in Thailand.
Moats are no longer a significant tool of warfare; however, in some cases a moat may still serve as a line of defense from other threats, as well as a number of other creative uses. A moat wide and deep enough can prove an obstacle to armoured fighting vehicles.
The Catawba Nuclear Station, for instance, has been constructing a concrete moat around some of the plant (other sides of the plant are bordering a lake). The moat is a part of industry wide added precautions after the September 11, 2001 attacks. Related individuals have made a point to claim that the moat is not connected to the new MOX fuel that the plant will be receiving.
"The concrete moat under construction at the station south of Charlotte has little to do with the utility's plans to start burning mixed-oxide fuel containing small amounts of weapons-grade plutonium next spring. Designed to prevent everything from passenger cars to military tanks from getting too close to the reactor, the moat is part of a post-Sept 11, 2001 security upgrade"
Moats rather than fences separate animals from spectators in many modern zoo installations. Moats were first used in this way by Carl Hagenbeck at his Tierpark. The structure, with a vertical outer retaining wall rising directly from the moat, is an extended usage of the ha-ha of English landscape gardening.
In 2004 plans were suggested for a two-mile moat across the southern border of the Gaza Strip to prevent tunnelling from Egyptian territory to the border town of Rafah .
In 2008, city officials in Yuma, 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.