The most durable and convenient of the Roman roads were thus composed: — The direction and breadth were first marked out by two shallow parallel furrows or trenches (sulci) from 15 to 8 feet apart, according to the importance of the via. The loose earth between the trenches was then taken away, and the soil farther removed until a sufficiently solid foundation was reached upon which to deposit the materials of the bed: — if from any cause, such as swampiness, no such natural basis was attainable, piles (fistucationes) were driven. Above the natural or artificial basis (the gremium) four strata were laid, of which the first (statumen) consisted of stones about three times the size of those employed by us in Macadamizing; next came the rudus, broken stones cemented with lime (answering to our rubble-work) — this was generally nine inches thick, and densely rammed. Then came the nucleus of broken earthen-ware, six inches thick, and also cemented with lime. Lastly came the true pavement, (pavimentum) which was composed of irregular polygons of silex, commonly basaltic lava. These blocks, however, were fitted together with great nicety, and presented just such an appearance as do our best built polygonal stone walls. The centre of the way was slightly elevated, as with us, above the curb-stones. Now and then, in cities, rectangular slabs of softer stone were substituted for the irregular lava polygons — and here the resemblance to the favorite modern mode was nearly complete. When the road or street passed over or through solid rock, the statumen and rudus were neglected, but the nucleus was never dispensed with. On each side of the way were elevated foot-paths, gravelled, and well supported; and at regular intervals were stone blocks, corresponding to our own steps, for the convenience of horsemen or carriages. Our mile-stones were also employed.
We are aware that all this is very school-boyish information — but we venture to place it before our readers by way of fairly collating the ancient and modern ideas on the general topic of road-making, and by way, also, of insisting on the observation with which we commenced — that it is exceedingly remarkable how little we have done to advance an art of so vast an importance, notwithstanding the continuous endeavors which have been made, and are still making, to advance it.
The Roman road (and our own quadrangular stone-block pavement is but a weak imitation of it) is beyond doubt exceedingly durable; and, so far, wherever the experiment has been tried, it has fully succeeded. By so far we mean so far as concerns durability. The objections are first, its cost, which is very great when the proper material is employed; and secondly the street din which is wrought by the necessity of having the upper surfaces of the blocks roughened, to afford a hold for the hoof. The noise from these roughened stones is less, certainly, than the tintamarre proceeding from the round ones — but nevertheless is intolerable still. The first objection (cost) is trivial where funds are at command; for in the end this species of pavement is the cheapest which has ever been invented, or probably ever will be invented — for repairs are scarcely needed at all. But it is cheap only in a save-at-the spigot understanding of the term — for our second objection is one of a vital importance. The loss of time (not to mention temper) through the insufferable nuisance of street-noise in many of our most frequented thoroughfares, would overwhelm all reasonable people with astonishment if but once fairly and mathematically put; and that time is money — to an American at least — is a proposition not for an instant to be disputed. Nor have we dwelt upon the vast inconvenience, and often fatal injury resulting to invalids from the nuisance of which we complain — and of which all classes complain, without ever mentioning the necessity of getting it abated.
It is generally admitted, we believe, that as long as they last, the wooden pavements have the advantage over all others. They occasion little noise (we place this item first and are serious in so placing it as the most important consideration of all); they are kept clean with little labor; they save a great deal in horse power; they are pleasant to the hoof and thus save the health of the horse — as well as some twenty or thirty per cent. in the wear and tear of vehicles — and as much more, in time, to all travellers through the increased rapidity of passage to and fro.
The first objection is that of injury to the public health from miasmata arising from the wood. Whether such injury actually does occur is very questionable — but there is no need of mooting the question, since all admit that the source of miasma (decay) can be prevented. It is demonstrated that by the process very improperly called Kyanizing (since Kyan has not the slightest claim to the invention) even the greenest wood may be preserved for centuries, or if need be for a hundred, or far more. The experiments by which this effect is, as we say, demonstrated, have been tried in every variety of way, with nearly identical results. Blocks properly prepared, for example, were subjected for many years, in the fungus pit of the dockyard at Woolwich, England, to all the known decomposing agents which can ever naturally be brought to act against a wooden pavement, and yet were taken from the pit, at the close of the experiments, in as sound a condition as when originally deposited.
The preservative agent employed was that of corrosive sublimate — the Bi-Chloride of Mercury. Let a pound of the sublimate be dissolved in fifteen or sixteen gallons of water, and a piece of wood (not decayed) be immersed for seventy-two hours in the solution, and the wood cannot afterwards be rotted. An instantaneous mineralization can be effected, if necessary, by injection of the fluid in vacuo into the pores of the wood. It is rendered much heavier, and more brittle by the process, and has altogether a slightly metallic character.
The cost of the Bi-chloride of Mercury is we presume, at present, something less than one dollar per pound — but the cost would be greatly reduced should the mineralizing process occasion an unusual demand. The South American quicksilver mines, now unworked, would be put into operation, and we should get the article, perhaps, for forty or even thirty cents per pound. But even now the cost of Kyanizing is trifling in comparison with that of cutting, squaring, and roughening stone — to say nothing of the difference in cost between wood itself, and such stone as our present pavements demand.
Decay being thus prevented, all danger from miasma is of course to be left out of the question; and although it has been frequently asserted that the mercurial effluvium is injurious to the health — the assertion has been as frequently refuted in the most positive and satisfactory manner. The mercury is too closely assimilated with the wooden fibre to admit of any perceptible effluvium. Even where sailors have lived for months in the most confined holds of vessels built of mineralized wood, no ill consequences have been found to arise.
We write this article with no books before us, and are by no means positive about the accuracy of our details. The general principles and facts, however, are not, we believe, matters of dispute. We confess ourselves, therefore, at a loss to understand how, or why it is, that a Kyanized wooden pavement to a limited extent, has not been laid (if only by way of a forlorn-hope-like experiment) in some of our public thoroughfares. Or are we merely ignorant of the case — and has the experiment been fairly tried, and found wanting ?