The earliest pavements of ancient times consisted of irregular dressed blocks of stone more or less accurately fitted together. The form and size of the blocks have varied greatly from time to time, a fact which has given rise to different classes of pavementi. A few of these will be briefly described.
The Roman roads so frequently referred to by modern writers are the earliest examples of stone-block pavements. The details of construction varied somewhat, but as a rule they were about as follows: The foundation was laid in a trench about 3 feet deep, with no attempt at underdrainage. The base was formed of one or sometimes two courses of large flat stones laid in lime mortar, and was usually about 15 inches thick. Upon this was laid a 9-inch course of small fragments of stone imbedded in lime mortar, the intention of this course apparently being to bind together the tops of the large stones in the course below. Next was laid a 6-inch layer of concrete, apparently to make a smooth bed to receive the stones of the top course. The wearing surface consisted of closely-jointed, irregular-shaped stones, about 6 inches thick. The total thickness of the road was about 36 inches. In and near the cities, the top course was formed of irregular blocks of basalt, porphyry, or lava which had a top area of 4 or 5 square feet and a thickness of 12 to 15 inches, and which were dressed and fitted together with extreme accuracy and were imbedded in cement. These ancient pavements have aptly been described as "masonry walls laid on their sides." The Romans seem to have located their roads in straight lines, running them toward prominent land-marks without much regard to the topography or to natural obstacles. They were wasteful of materials and labor, which, however, cost nothing but the lives of captives who were forced to build these roads for the armies of their captors. The results were roads which are remarkable chiefly for their cost, and which were inferior to modern pavements cost ing only one quarter to one eighth as much. The durability of these roads does not seem so remarkable when it is remembered that the traffic was light, and consisted mostly of footmen, unshod horses, and ox-carts having wooden wheels, and also that probably the surface of the road was kept covered with earth two or three inches deep.
The earliest dressed stone-block pave ment in this country was the Russ patent laid on Broadway, New York City, in 1849. This consisted of a 6-inch natural-cement concrete foundation on which was laid rectangular granite blocks, 10 to 18 inches long, 5 to 12 inches wide, and 10 inches deep, the sides of the blocks making an angle of 45 degrees with the line of the street.
In some cities having no cobble stones but having comparatively plenty of even bedded sandstone or limestone, the streets were paved by laying rough rubble stones flatwise, the stones being 4 to 6 inches thick and having a top surface of 4 to 6 square feet. The irregttlar joints between the stones were filled with spalls. The blocks chipped on the edges,
wore round on top, and readily got out of place, thus making an exceedingly rough pavement.
In Europe the first modem pavements were made of rectangular blocks having several square feet of top surface, which were laid lengthwise of the street; but as traffic increased it was found that the long joints, being parallel to the direction of the travel, rapidly wore into ruts and the pavement became rough and uneven. To obviate this, the blocks were made square and were laid with their sides at an angle of 45 degrees with the line of the street. It was soon discovered, however, that large blocks were not suitable for heavy traffic, as it was difficult to bed them so they would keep their place, and as their large surface did not afford a good foothold for horses. This led to the use of small square blocks laid with their edges parallel and perpendicular to the line of the street. For many years this form of pavement has been very common in the cities of Europe, the blocks usually having a top surface 5 to 7 inches square and a depth of about 6 inches. This form of pavement seems to have been used first in the city of Brussels, Belgium ; and in this country is known as Belgian pavement.
The Belgian block was introduced in this country about 1850, and for a time was much employed. The objections to the Bel gian pavement are : 1. On account of the size and form of the blocks, it is difficult to keep them in place; 2, the blocks are of such a form as to give a poor foothold to horses; and 3, there is always a considerable length of joints parallel to the line of travel, which causes ruts to form in the pavement. Belgian blocks have usually been laid with their sides perpendicular and parallel to the sides of the street; but if a square block is to be used, it should be laid in courses diagonal to the street. so that no joints shall be parallel to the line of travel, a method which would add some extra expenbT. The Belgian block has been discarded in this country for the ob long block.
This pavement consisted of stone blocks having a hexagonal top surface, the joints running perpen dicular to the street being comparatively wide and those parallel with it being comparatively narrow. About 1869 a considerable amount of this pavement was laid in New York city and Brooklyn, at a cost of about $7.00 per square yard.
At present the only stone paving blocks employed in this country are 3 to 4 inches wide, S to 10 inches long, and 7 to 8 inches deep, and these are laid with their longest dimension perpendicular to the line of the street.
Stone-block pavements of any and all kinds are at present con structed much less frequently than formerly, brick or asphalt being employed instead; but it is probable that stone blocks will con tinue to be employed, at least for some time, on heavy traffic streets, and for medium traffic streets where suitable stone is plen tiful and brick is expensive.