Pavement (Lat. pavimentum, from pavire, to beat or ram down), a covering of stone or other hard material for roads, walks, and floors of houses. The earliest mention of paved highways is of those prepared by Se-miramis, according to the inscription which she set up, recorded by Valerius Maximus. Isido-rus says the Carthaginians had the first paved roads. The streets of Rome were not paved in the time of its kings, but the Appian way was constructed by Appius Claudius 200 years after their expulsion, and many of the streets are known to have been paved with stone in the 4th and 5th centuries after the building of the city. Pavements of blocks of lava worn into ruts by the wheels of carriages are met with in Herculaneum and Pompeii. From the descriptions of pavements given by Vitruvius, together with the poem of Statius on the Via- Domitiana and the fragments of ancient paving still remaining, a very clear idea may be formed of the care given by the Romans to the construction of their famous roads. These were laid out with a width of from 8 to 15 ft. by excavating a shallow trench along each side. The space between these was then dug down to a solid bed, or if this could not be reached piles were driven to support the materials of the road.

The lowest course was of broken stones, none smaller than the fist; over these was a course 9 in. thick of rubble work, or broken stones cemented with lime, well rammed; over this was a course 6 in. thick of finer materials, chiefly broken bricks and pieces of pottery, also cemented with lime; and upon this was laid the pavimentum, which consisted of large polygonal blocks of the hardest silicious stones, sometimes of basaltic lava, of irregular form and nicely fitted together in a sort of mosaic. In the cities the "slabs of stone were sometimes rectangular and of softer material, as in the forum of Trajan, which was paved with travertine. In every instance great care was taken to fit the stones to each other so as to produce a perfectly even surface. The floors of Roman houses were paved with pieces of bricks, tiles, stones, etc.; sometimes with tiles ground to powder and mixed in with mortar; and again with pieces of marble imbedded in a cement ground; and well beaten or rammed down, whence the name pavimentum.

Mosaic pavements were first made in the time of Sulla, by whom, according to Pliny, one was constructed in the temple of Fortune at Prse-neste. They became very common in the houses of Pompeii, and were there produced with great taste in a variety of beautiful patterns, in marble of different colors, in tiles, and even glass, set in a fine cement and laid upon a deep bed of mortar. Some of the designs were of figures and scenes in actual life, being really pictures in mosaic. An account was presented to the British association in 1850, by Prof. Buckman, of an ancient Roman pavement discovered at Cirencester, in which appeared a medallion of Flora with a head dress and flowers of verdigris green when first uncovered. This being scraped off, the portion of the pavement beneath was found to be a beautiful ruby glass, the color of which was derived from peroxide of copper, and this by decomposition had become converted externally into the green carbonate of copper. - Though the paved roads of the ancient Romans surpass all other structures of the kind that have been made by civilized nations since their time, there are found in Peru remains of works of a similar kind of unknown age, and exceeding them in grandeur and extent.

Such were the great roads from Quito to Cuzco, and continued south toward Chili, laid out through mountainous and almost impassable regions for distances variously estimated from 1,500 to 2,000 m., and about 20 ft. in breadth, They were built of heavy flags of freestone, and in some parts covered with a bituminous cement, which time has made harder than the stone itself. In Mexico, among the ruins of Palenque, are also found pavements of large square blocks of stone constructed with great skill and nicety. - In Europe during the middle ages comparatively little attention was given to the paving of streets and roads. CordQva in Spain was paved in 850 by Abderrahman II. Streets in Paris were first paved in 1184 by Philip Augustus. In 1832, in excavating for a sewer in the rue St. Denis, this ancient pavement was met with, and a little below this the still more ancient roadway of gravel of the period of the Roman emperors. There were a few paved streets in England before the time of Henry VII. London was first paved in 1533, but many streets continued in a perilous condition by reason of deep pits and sloughs through the whole of the 16th and 17th centuries.

Holborn was paved by royal command in 1417; but the great market of Smith-field remained without pavement 200 years longer. - In modern times various methods and materials of paving have been employed. In Holland all the streets are paved with bricks, which are also used for the same purpose in Venice. They obviously lack the strength and durability required for the passage over them of heavy loads. In other cities, instead of the broad flat stones used by the Romans, rounded pebbles called cobble stones, found among the gravel of the diluvium or along sea and river beaches, have been very generally used. These, when of hard stone, closely set, and well rammed down in a bed of gravel and sand, form an economical and very durable pavement, which gives secure footing to horses and is easily repaired. Blocks of wood have been at times in some repute, but they have proved objectionable on account of soon becoming slippery, particularly when wet, and also of their tendency to decay. They were commonly cut in hexagonal prisms and set upright, so that the wear came across the ends of the grain. Hemlock, being cheap, was usually selected for the purpose in America, where however this form of pavement has been generally abandoned.

A part of Broadway, New York, between Chambers and Warren streets, was laid with hexagonal wooden pavement in 1835. Different foundations were tried, such as cobble stones, flagging, and macadam. The surface was coated with tar and gravel. The Nicolson pavement was introduced into Boston in 1848, and was among the first wooden pavements extensively used. It consists of a foundation of hemlock, spruce, or pine boards, laid flat upon the ground, upon which blocks of similar wood or of chestnut, from 4 to 6 in. long and wide, and from 2 to 3 in. thick, are set with the grain vertical. Between the blocks, running across the street, inch boards are set on edge, the upper edge being a little below the surface of the blocks, and the grooves so formed are filled with coarse gravel. The blocks are either soaked in melted asphalt, or the hot material is turned over the whole and made to fill the interstices. If the blocks and foundation boards were thoroughly kyanized and boiled in the asphalt till saturated, the pavement would undoubtedly be rendered very durable, especially if a foundation of concrete were first laid. There are other forms of wooden pavement which are held in place by an ingenious locking together, and answer a good purpose as long as the material resists decay.

Kyanizing and proper saturating with coal tar or asphalt can always be applied to these pavements; and conscientious attention to preparing a proper foundation will secure satisfactory results. It may be remarked that honesty in the performance of contracts for paving is an element without which no pavement can be expected to have a reasonable degree of permanence. - The pavements most common in Europe are ashlar, macadam, concrete both hydraulic and bituminous, and Neufchatel and other asphalt pavements. The common ashlar is composed of square blocks of stone, usually granite, about 12 in. deep and 10 or 12 in. long, by 5 to 7 in. wide. A pavement of granite similar to this, though not quite so deep, was some years ago placed in Broadway, New York, called Russ pavement. It proved impracticable on account of slipperiness, and after various attempts to overcome this by cutting grooves, it was replaced by one made of thinner stones, called the Guidet pavement. In this the stones are 6 or 8 in. deep, and about 12 in. long by 4 in. wide. They are set on edge, and in wearing do not form large smooth surfaces like the ashlar or Russ, and consequently afford greater protection against the horses' slipping.

If they were laid upon a concrete foundation, the pavement would not need resetting as often as when laid upon common gravel and sand. This pavement is now extensively used for the main thoroughfares of cities. Many streets of New York and other American cities have the so-called Belgian pavement, consisting of small cubical blocks, generally of trap rock, which has proved very durable. Cobble-stone pavement has been much used in many cities of the United States, and when made of stones of nearly equal size and 4 or 5 in. in diameter, laid upon a good bed of gravel and sand, makes a very good pavement for a few years. The ease and cheapness with which it may be repaired cause it to be retained in many localities where cobble stones can be easily procured; but the jolting and noise of vehicles driven over it make it objectionable for streets having much traffic. - The early stone roads in France were formed of beds of flat stones covered with broken stones, large below and smaller above. About 1760 Tresaguet discarded the flat stones except on marshy ground, and substituted stone blocks on an arched bed. This method continued till the early part of the present century, when. the large stones of Tresaguet were replaced by a crust of small broken stones laid directly on the ground.

In 1816-19 Macadam made many roads of this kind in England, and his success caused his name to be given to the system. The roads made by him were however inferior to those made in France by the same process. He disregarded too much the nature of the soil, and the defects which followed resulted in the advocacy by Telford of a return to the use of large stones at the bottom on soft ground. Flagging is sometimes laid in connection with macadamized pavement in rows far enough apart to support the wheels of carriages, by which the cutting of the road into ruts is avoided, while the coating of pounded stone need not be so great. Such a road may be seen on parts of the old turnpike between Albany and Schenectady, N. Y. - Within a few years increased attention has been given to the construction of asphalt pavements, particularly in France, and when they are properly laid upon a solid concrete foundation (and they ought to be laid upon no other) they probably form the best roadway that can be constructed. Pavements called asphalt had been laid down in different places in Europe and America, but they did not answer the purpose of either a roadway or sidewalk. They were chiefly a sort of asphalt concrete, made by simply mixing melted bitumen with coarse gravel or pounded stones.

The more volatile portions of the bitumen being retained, they would gradually pass away, and a crumbling of the road bed would be the final result, preceded during the summer months by the formation of a " poultice." But more attention having been paid to the conditions in which the bitumen is used, a decided advance has been made, and to a greater extent in France than elsewhere. A very good pavement can be made by raising the bitumen to 250° or 300° to expel the volatile portions, and using the residue to fill voids in coarse gravel or broken stone; but a better material is now used in Europe, and also introduced into the United States, in the form of an asphaltic limestone found in the Val de Travers in Switzerland, and exported from Neufchatel, and known as Seyssel or Neufchatel asphaltic rock. A good substitute is also made in the United States by mixing such minerals as grahamite or albertite with Trinidad asphalt, and combining this with calcareous sand or similar material. The Seyssel rock is a native limestone, composed of pure carbonate of lime impregnated more or less with bitumen, generally containing from 92 to 93 per cent, of limestone and 7 to 8 per cent, of bitumen.

Less pure varieties are found in the volcanic region of Auvergne, and contain clay, silica, magnesia, iron, etc. The Seyssel rock has a fine-grained irregular fracture, with a sonorous sound like ordinary limestone at common temperatures; but at 120° F. it may be flattened; at 160° it begins to crumble, and at 212° the disintegration is complete. Its average specific gravity is 2*235. In Paris this rock is used in two forms: in an unmixed or pure condition for road beds of streets, and mingled with bitumen in different proportions for sidewalks and parks,. the artificial bituminous mixture being called "mastic of asphalt," while the unmixed rock is called " asphalt." When it contains less than 6 per cent, of bitumen, it is not regarded as fit to be worked. The road bed is formed by beating the earth compactly, care being taken to insure good drainage. A concrete of gravel or broken stone in a matrix of hydraulic cement is then laid from 4 to 8 in. or even more in thickness, depending on the nature of the ground, and is allowed to set and become dry upon the surface. Upon this the prepared asphalt is spread.

The rock is crushed by being first broken into pieces, then passed between rollers armed with strong teeth, and afterward between smooth cylinders; it is then roasted in shallow sheet-iron pans, or in revolving cylinders. It is at first heated to 160° or a little upward until it begins to crumble, and then raised to 250° or 300°, the operation requiring about an hour and a half. The concrete bed must be dry before the asphalt is laid upon it, for if not steam will be formed and prevent the consolidation of the material. The drying may be hastened by covering with hot ashes or hydraulic lime. The asphalt, which the heat has reduced to the form of a powder, is then spread uniformly over the surface of the concrete bed to the thickness of 2 or 2 1/2 in., so that when compacted it will be from 1 1/2 to 2 in. thick. The packing is principally done by hand, with hot iron pestles, raised nearly to redness. A coat of dry sifted powder is then spread over to fill up inequalities of surface, and a flat iron heated nearly to redness is passed over the whole. Pollers weighing from 500 lbs. to a ton and a half are often used, in conjunction with the hand packing, but their utility in increasing the solidity is doubtful.

After the packing has been completed the road may be opened in a few hours for vehicles of all kinds. The grahamite asphalt pavement company of New York make a substitute for the Seyssel rock by combining about 20 per cent, of asphalt mixture with 80 per cent, of calcareous sand, which should contain at least 20 per cent, of carbonate of lime. The asphalt mixture is composed of varying proportions, depending on location and climate, of Trinidad asphalt and grahamite, a firm con-choidal fracturing carbonaceous mineral found in large quantities in West Virginia, and first accurately described and named by Prof. Henry Wurtz. From samples that have been laid in some of the streets of New York it may be expected that this will make a good road pavement when laid upon a good concrete foundation. It should be a well recognized rule that no asphalt road shall ever be attempted or allowed to be laid without the road bed being first covered with a layer of hydraulic concrete sufficiently thick to withstand the pressure of the heaviest carts and drays.