Research Results For 'Drawbridge'

BARBICAN

A barbican is a tower or advanced work defending the entrance to a castle or city, for example at a gate or bridge. It was often large and strong, having a ditch and drawbridge of its own. The term barbican was also applied to an opening in the wall of a fortress, through which missiles were discharged upon an enemy.
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CASTLE

A castle (from the Latin castellum, meaning fortress) was a stone defensive building. The concept of castles was introduced to the British by the Normans and replaced the earlier Saxon burh. The castle underwent many changes, its size, design, and construction being largely determined by changes in siege tactics and the development of artillery. Outstanding examples are the 12th-century Krak des Chevaliers, Syria (built by crusaders); 13th-century Caernarfon Castle in Wales; and the 15th-century Manzanares el Real in Spain. The main parts of a typical castle are the keep, a large central tower containing store rooms, soldiers' quarters, and a hall for the lord and his family; the inner bailey or walled courtyard surrounding the keep; the outer bailey or second courtyard, separated from the inner bailey by a wall; crenulated embattlements through which missiles were discharged against an attacking enemy; rectangular or round towers projecting from the walls; the portcullis, a heavy grating which could be
let down to close the main gate; and the drawbridge crossing the ditch or moat surrounding the castle. Sometimes a tower called a barbican was constructed over a gateway as an additional defensive measure. Early castles (11th century) consisted of an earthen hill (called a motte) surrounded by wooden palisades enclosing a courtyard (called a bailey). The motte supported a wooden keep. Later developments substituted stone for wood and utilised more elaborate defensive architectural detail. After the introduction of gunpowder in the 14th century, castles became less defensible and increases in civil order led to their replacement by unfortified manor houses by the 16th century. Large stone fortifications became popular again in the 18th century, particularly those modelled after the principles of fortification introduced by the French architect Vauban, and were built as late as the first half of the 19th century. In the late 19th century, castle-like buildings were built as residences for the wealthy as part of the Romantic revival in Europe and America.
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BRIDGE

A bridge, a structure of stone, brick, wood, iron or other material, affording a passage over a stream, valley, or the like. The earliest bridges were probably the trunks of trees. The simplest form of bridge is known as a clapper-bridge and consists of planks or slabs of stone which rest on piles of stones.

The arch seems to have been unknown amongst most of the nations of antiquity. Even the Greeks had not sufficient acquaintance with it to apply it to bridge building. The Romans were the first to employ the principle of the arch in this direction, and after the construction of such a work as the great arched sewer at Rome, the Cloaca Maxima, a bridge over the Tiber would be of comparatively easy execution. One of the finest examples of the Roman bridge was the bridge built by Augustus over the Nera at Narni, the vestiges of which still remain.

It consisted of four arches, the longest of 43 meters span. The most celebrated bridges of ancient Rome were not generally, however, distinguished by the extraordinary size of their arches, nor by the lightness of their piers, but by their excellence and durability. The span of their arches seldom exceeded 20 or 25 meters, and they were mostly semicircular, or nearly so.

The Romans built bridges wherever their conquests extended, and in Britain there are still a number of bridges dating from Roman times. One of the most ancient post-Roman bridges in England is the Gothic triangular bridge at Croyland, in Lincolnshire, said to have been built in 860, having three archways meeting in a common centre at their apex, and three roadways. The longest old bridge in England was that over the Trent at Burton, in Staffordshire, built in the twelfth century, of squared freestone, and pulled down in the 19th century. It consisted of thirty-six arches, and was 47 meters long.

Old London Bridge was commenced in 1176, and finished in 1209. It had houses on each side like a regular street until 1756-58. In 1831 it was altogether removed, the new bridge, which had been begun in 1824, having then been finished.

The art of bridge-building made no progress after the destruction of the Roman empire until the eighteenth century, when the French architects began to introduce improvements, and the constructions of Perronet (Nogent-sur-Seine; Neuilly; Louis XVI bridge at Paris) are masterpieces. Some of the stone bridges built in later times far surpass those of older times in width of span.

Stone bridges consist of an arch or series of arches, and in building them the properties of the arch, the nature of the materials, and many other matters have to be carefully considered. It has been found that in the construction of an arch the slipping of the stones upon one another is prevented by their mutual pressure and the friction of their surfaces; the use of cement is thus subordinate to the principle of construction in contributing to the strength and maintenance of the fabric. The masonry or rock which receives the lateral thrust of an arch is called the abutment, the perpendicular supports are the piers. The width of an arch is its span; the greatest span in any stone bridge is about 75 meters. A one-span bridge has, of course, no piers.

In constructing a bridge across a deep stream it is desirable to have the smallest possible number of points of support. Piers in the waterway are not only expensive to form, but obstruct the navigation of the river, and by the very extent of resisting surface they expose the structure to shocks and the wearing action of the water. In building an arch, a timber framework was used called the centre, or centering. The centering had to keep the stones or voussoirs in position until they were keyed in, that is, all fixed in their places by the insertion of the key-stone.

The first iron bridges were erected from about 1777 to 1790. The same general principles apply to the construction of iron as of stone bridges, but the greater cohesion and adaptability of the material give more liberty to the architect, and much greater width of span is possible. At first iron bridges were erected in the form of arches, and the material employed was cast-iron; but the arch has been generally superseded by the beam or girder, with its numerous modifications; and wrought-iron or steel was likewise found to be much better adapted for resisting a great tensile strain than cast-metal.

Numerous modifications exist of the beam or girder, as the lattice-girder, bow-string-girder, etc; but of these none is more interesting than the tubular or hollow-girder, first rendered famous from its employment by Robert Stephenson in the construction of the railway bridge across the Menai Strait, and connecting Anglesey with the mainland of North Wales. This is known as the Britannia Tubular Bridge. The tubes are of a rectangular form, and constructed of riveted plates of wrought-iron, with rows of rectangular tubes or cells for the floor and roof respectively. The bridge consists of two of these enormous tubes or hollow beams laid side by side, one for the up and the other for the down traffic of the railway, and extending each to about a quarter of a mile in length.

Other tubular bridges of interest are the Conway Bridge, over the river Conway, an erection identical in principle with the Britannia Bridge, but on a smaller scale; the Brotherton Bridge over the river Aire; the tubular railway bridge across the Damietta branch of the Nile, which has this peculiarity, that the roadway is carried above instead of through the tubes. The Victoria Bridge over the St Lawrence at Montreal, originally tubular, is no longer so, the upper portion having been reconstructed with an open track. It is nearly two miles in length, or about five and a half times as long as the bridge across the Menai Strait. A girder railway bridge across the Firth of Tay at Dundee was opened in 1887, being the second built at the same place, after the first had given way in a great storm. It is 2 miles 73 yards long, has 85 spans, is 77 feet. high, and carries two lines of rails. The bridge over the Firth of Forth at Queensferry, was completed in 1889, and was the largest bridge built on the cantilever principle and was the first very notable example.

A cantilever is a structure the main feature of which is a projecting arm jutting out over the space to be spanned and supporting the roadway; and two cantilevers may be made to meet directly, or the space between may be bridged over by a girder connected with both. The cantilever principle has the advantage that it may be employed where there might be great difficulties in the way of a bridge otherwise constructed, since the projecting arm may be built out from either side of the river or other opening to be crossed, and at a great height if necessary. In some cases a bridge with an arch or arches of wrought iron or steel is preferred chiefly or solely because such a structure has a more handsome appearance than some other bridges.

American engineers have been very successful as builders of iron bridges, adopting various forms of girder, and constructing also some splendid bridges, with arches of great span, built up of wrought iron and steel.

Suspension-bridges, being entirely independent of central supports, do not interfere with the river, and may be erected where it is impracticable to build bridges of any other kind. The entire weight of a suspension-bridge rests upon the piers at either end, from which it is suspended, all the weight being below the points of support. Such bridges always swing a little, giving a vibratory movement which imparts a peculiar sensation to the passenger. The modes of constructing these bridges are various. The roadway is suspended either from chains or from wire-ropes, the ends of which require to be anchored, that is attached to the solid rock or masses of masonry or iron. One of the earlier of the great suspension-bridges is that constructed by Telford over the Menai Strait near the Britannia Tubular Bridge, finished in 1825. The cable-stayed bridge is a type of suspension bridge in which the supporting cables are connected directly to the bridge deck without the use of suspenders.

Though the oldest bridges on record were built of wood, like the Sublician Bridge at Rome, or that thrown by Caesar across the Rhine, it is only in certain places and for certain purposes that wood was much used after 1800. In the 19th century Germany was the school for wooden bridges. Perhaps the most celebrated of all wooden bridges was that which spanned the Rhine at Schaffhausen in Switzerland. This was 364 feet in length and 18 feet broad. It was designed and executed by Ulric Grttbenman, a village carpenter, in 1758, and was destroyed by the French in 1799. In the United States, where timber was still in common use in the 19th century, the Trenton Bridge over the Delaware, erected in 1804; the bridge over the Susquehannah, etc were examples of wooden bridges.

Trestle Bridges, or bridges the roadway of which is supported on wooden trestles or frames, formed of a series of beams and braces and often built up to a great height, were common in America until recently. Certain kinds of bridges are known as movable bridges. The bascule, balance, counterpoise or drawbridge - in which the roadway may be raised and lowered in one or two pieces, - is a common form; and there are also swing bridges (also known as pivot bridges) - opening horizontally to let shipping pass; bridges constructed so as to roll horizontally on wheels or otherwise; bridges in which the movable part, carrying the traffic, is suspended from a high iron framework or cables, under which shipping passes; these forming transporter bridges, as the bridge across the Mersey between Runcorn and Widnes, etc.

Pontoon or floating bridges are formed of pontoons or boats over which the roadway is laid, there being often the means of making an opening for shipping. A flying bridge is simply a kind of ferry. The Tower Bridge, London, crossing the Thames, is a unique structure, a combined suspension and bascule bridge, opening in the centre to admit ships, and originally having an elevated footway for passengers, with lifts and stairs in two towers.

The Bailey bridge is a temporary bridge made of prefabricated steel parts that can be rapidly assembled. It is named after its inventor, the Englishman Sir Donald Bailey who designed the Bailey bridge during the early-mid 20th century.

CASTLE

A castle (from the Latin castellum, meaning fortress) is an edifice serving at once as a residence and as a place of defence, especially such an edifice belonging to feudal times. Castles differed somewhat at different times and in different places, but they had all several features of similarity. Early castles in Europe followed the basic Saxon burh design, ditches surrounding a raised earthen hill (the motte) surmounted with a wooden palisade enclosing a courtyard (called a bailey). The motte supported a wooden, defensive building known as the keep.

Later developments substituted stone for wood and utilised more elaborate defensive architectural detail. After the introduction of gunpowder in the 14th century, castles became less defensible and increases in civil order led to their replacement by unfortified manor houses by the 16th century. Large stone fortifications became popular again in the 18th century, particularly those modelled after the principles of fortification introduced by the French architect Vauban, and were built as late as the first half of the 19th century. In the late 19th century, castle-like buildings were built as residences for the wealthy as part of the Romantic revival in Europe and America.

The first defence of a castle was usually the moat or ditch, that sometimes comprised several acres; and behind it was the outer wall, generally of great height and thickness, strengthened with towers at regular distances, and pierced with loopholes through which missiles could be discharged at the assailants.

The main entrance through the outer wall was protected by the barbican, with its narrow archway, and strong gates and portcullis, and inside there were usually an outer and an inner court, and the strong more or less detached building known as the keep, which formed the residence of the owner and his family. This was the most strongly constructed of all the buildings, to which the defenders retreated only in the last extremity. In English Edwardian castles (so named from Edward III) the solid keep becomes developed into an open quadrangle, defended at the sides and angles by gatehouses and towers, and containing the hall and state apartments ranged along one side of the court. Around this inner court two or three lines of defence are disposed concentrically. Such castles frequently enclose many acres, and present an imposing appearance. The parts of a perfect Edwardian castle are: the inner bailey or inner court; the walls of the enceinte, single, double, or triple; the middle and outer baileys, contained between the walls; the gatehouses and posterns, or small doors in the wall; and the moat or ditch, which was usually filled with water. The walls were all strengthened by towers, either circular, square, rectangular, or multi-angular, projecting both outwards and inwards. Such towers were capable of being defended independently of the castle.

The gatehouses are distinct works covering the entrance; they contain gates, one or two portcullises, and loopholes raking the passage. From the front of these gatehouses the drawbridge was lowered over the ditch. The gateways had frequently a barbican attached. This was a passage between high walls, in advance of the main gate, and having an outer gate of entrance, which was defended by towers and the parapet connected with the main gateway. The top of the wall was defended by a battlemented parapet, and frequently pierced by cruciform loopholes.

Castles were known in Britain prior to the Norman conquest of 1066, but it was the Normans who developed the later and more familiar style of stone castle. The Normans' first castles, over five hundred of them in England, were Motte and Bailey designs made of wood. The first stone castle and the blueprint for further Norman castles was the Tower of London. After the death of William the Conqueror, the Norman lords switched from building a multitude of wooden castles, to instead building a single, large, stronger, more impressive stone castle based upon the Tower of London design.

Outstanding examples of castles are the 12th-century Krak des Chevaliers, Syria (built by crusaders); 13th-century Caernarfon Castle in Wales; and the 15th-century Manzanares el Real in Spain.
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DRAWBRIDGE

A drawbridge is a bridge with a lifting floor, such as were formerly used for crossing the ditches of fortresses, or any movable bridge over a navigable channel where the height of the roadway is insufficient to allow vessels to pass underneath. Modern drawbridges across rivers, canals, the entrances of docks, etc, are generally made to open horizontally, and the movable portion is called a bascule, balance, or lifting bridge, a turning, swivel, or swing bridge, or a rolling bridge, in accordance with the mode in which it is made to open. Swing-bridges are usually divided into two parts meeting in the middle, and each moved on pivots on the opposite sides of the channel, or they may move as a whole on a pivot in the middle of the channel. Rolling bridges are suspended from a structure high above the water, and are propelled backwards and forwards by means of rollers.
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