Popular Science Monthly/Volume 2/December 1872/How was Herculaneum Destroyed?
|HOW WAS HERCULANEUM DESTROYED?|
TRANSLATED FROM THE REVUE DES DEUX SONDES.
HISTORY points out marked differences between Herculaneum and Pompeii. The first, settled by the Greeks, was devoted to intellectual culture and refined leisure; the latter, of Oscan origin, concerned itself solely about commerce; one was inhabited by Romans of fortune, and loaded with favors; the other endured the hostility of Rome, and often incurred her chastisement. There is reason to believe that Herculaneum gave a model for many details of civilization to Pompeii, and we may safely assert that Pompeii taught Herculaneum nothing. Besides, the earthquake which was so fatal to Pompeii in the year 63, under Nero, did Herculaneum no injury; so that there a part of the buildings anterior to the empire, and houses of earlier style, which implies purer taste, must have been preserved. This conclusion is strengthened at the present day by the beauty of those objects collected at Herculaneum, and will be settled beyond question whenever the city itself shall be restored to light.
What was the fate of Herculaneum during the eruption of a. d. 79? What special phenomena were displayed on that side of Vesuvius? What causes buried a nourishing city in an instant out of sight of the inhabited world? It has been proved that Pompeii suffered an interment so incomplete that after a few days its inhabitants could recognize their dwellings, could encamp above and clear them out; Herculaneum, on the contrary, was buried so deep that the next day it was impossible to trace a vestige of it. The ready answer to all these questions usually is: "Lava worked all the ruin. Herculaneum was swallowed up under eighty feet of lava. If works of art, bronzes and pictures have been miraculously preserved, it was due to the impenetrable shield of lava, yielding only to a cutting tool, that protected them from the ravages of time." The explanation is tempting. Fancy pictures waves of fire rolling upon the city, rising like the tidal swell, surging in through doors and windows, sweeping around and moulding every thing, then slowly cooling, and preserving for posterity treasures that labor must unveil, repaid by their recovery in unharmed beauty.
This is really the opinion that all Europe holds, and even at Naples almost all visitors of Herculaneum declare that they have touched the lava with their own hands; and, in books written on the Vesuvian cities, more than one traveller affirms as positively that the difficulty of cutting the lava presents the chief obstacle to the disinterment of Herculaneum. How can one venture to meet such convictions by asserting that water, not fire, overwhelmed Herculaneum; that it was not a torrent of glowing lava, but a flood of mud and wet ashes that filled the city? How uproot a prepossession so deep that the works of geologists and savants have failed to shake it? Dufrénoy proved that water alone swept over Herculaneum heaps of scoria and pumice crumbled from La Somma; Dyer, Overbeck, Ernst Breton, and others, have affirmed in various languages, to no purpose, that nothing but ashes, wet to paste and hardened by pressure, covered over Herculaneum: no one heeded them, and the blame continues to be thrown on the lava, which makes excavation so costly and laborious.
But every one knows the nature and effects of lava. Lava is an incandescent mass, of so high temperature as to absorb and melt all fusible bodies; forced out from the fissures of the crater by irresistible expansive power, this mass rolls on in a fiery river, burning up every thing in its path; cooling slowly, it grows as hard as porphyry or adamant. Now, I appeal to the recollection of all who have ascended Vesuvius during those lava-flows that succeed an eruption, and continue for weeks or months even. What happens to-day, if studied with a little good sense and reflection, can enlighten us on what must have happened eighteen centuries ago. For instance, we have seen how slow lava-currents, remote from the vent of escape and cooled by contact with the ground and air, flowing around country-houses, level and consume them, with a sudden flaming up of roofs and floors. How could the stuccoes and the marble statues of Herculaneum remain unharmed, in their original color, free from crack or splinter, if they had been enveloped in lava? We have seen metals by mere contact melt and vanish in that viscous paste, which glows like fused iron or glass gushing from a furnace. How, then, do we find in Herculaneum articles of silver, bronze statues, leaden vases, with their shapes, their relief, their ornaments and polish uninjured? The bronzes of Herculaneum are even better preserved than those of Pompeii, being distinguished by their freshness of surface, their lustre, and dark and even tone, while the Pompeian bronzes have been attacked by sulphurous fumes, and eaten on the surface, and have taken on an agreeable ultra-marine blue tint, like that of sulphate of copper.
Other facts of the same kind are quite as puzzling. The guides amuse strangers with an experiment; breaking off a bit of lava with an iron-pointed stick, they let it cool on the ground, and stamp a penny on it, to get an impression of the coin. If the trial is made too quickly, the copper melts, and the coin, instead of leaving its image, disappears and mingles with the rest of the lava. How, then, do we find at Herculaneum so many ancient silver or copper coins, not merely undestroyed, but not even changed, by those waves of lava which attain a concentrated heat beyond all measurement? We know, too, that the ancients used colors with a mineral base in decorating their buildings; they will stand dampness from the earth, but the touch of fire changes their nature; the partial fires that have left traces in Pompeii have in some places altered the blue to gray, and the red to yellow, and Neapolitan artists in our time well understand the very simple method of producing what is called burnt-yellow, by exposing minium to the action of fire. How, then, do the houses uncovered at Herculaneum present such exquisite colors? How is it that the ultra-marine blue and the vermilion-red, covering whole walls, keep a freshness and smoothness that contact with a burning substance must necessarily have destroyed? Then, too, on Vesuvius I have seen trees just touched by the lava-flow take fire like matches, throw out a blazing jet, and fall at once, as if struck with lightning. Why have the beams and floors and sills of Herculaneum, instead of crumbling into ashes, slowly decayed in their places in the bosom of the earth, leaving no holes nor fractures? Why are they found blackened like oak-timbers that have been sunk in the mud for ages, like the piers of bridges and the piles of old docks at Carthage, and the wood brought down by the Jordan and thrown out by the Dead Sea, saturated in it with chloride of sodium? How is it that every thing proves their decomposition to come only from the effects of time? How has the wood kept its character and color in those parts pierced by spikes and nails, in other words, protected from dampness by iron rust? How do we find manuscripts written on the soft fibres of papyrus-reed, when lava must infallibly have consumed them, and dispersed their ashes like those of a sheet of paper thrown on burning coals? Why has this kind lava, in like manner, respected fruits, nuts, almonds, linen, silk, lamp-wicks found in hundreds, and so many very combustible articles which have merely turned black, when they usually vanish, without the least trace, in the feeblest flame?
This refutation by absurdity might be urged with multiplied arguments. Indeed, very slight reflection suffices to show that fire could not have played any part in the destruction of Herculaneum, and that if lava, the most terrible destroying agent next to lightning, had made its way into the city, we should scarcely recognize a few blackened stones, smashed bricks, and calcined marbles. But, to say all in a word, I state that on a late tour I examined the ground of Herculaneum, in the parts made accessible by excavation, with particular care. I could not find a square inch of lava! Every thing is ashes, nothing but ashes, and these ashes have been hardened by three agents—water, pressure, and time. It is exactly this hardness, which is not to be conceived of as very great, that has deceived visitors, particularly in the underground galleries dug out in exploring the theatre. The descent is by stairways damp with exudations from the streets of Portici; overhead is heard the rolling of vehicles; we pass through tunnels polished with rubbing; we see on the smoky arches the smudge of torches, collecting for centuries; we shudder at the appalling gloom, and seem buried in the bowels of the earth. In a word, the passage impresses the imagination as strange and awful, and we reassure ourselves perforce with the thought that these galleries are hewn in lava, and beyond danger of caving in; but a scratch of the nail on this supposed lava betrays the fact that it is friable and yielding, being-only hardened ashes. In one of these tunnels, which are pretty regularly cut out, the guides show the print of a human face. We wonder at the unchanging solidity of a substance which once so finely moulded the objects it surrounded. Still, if you try to cut with a knife, not into the impression itself, but into the parts next it, you are amazed to find that nothing is easier, and that it is all mere solidified ashes.
One street of Herculaneum, in the outskirts, on the side nearest the sea, has been regularly excavated, and several houses cleared out—that called the house of the skeleton, the house of Argus, some shops, a slave-prison, and others—all is in the open air, and one can walk as in the streets of Pompeii. The space thus disentombed is from 3,000 to 4,000 square yards, a large-enough area for observations of the kind we are pursuing. Now no fragments of lava, not a vestige of it, are to be found there, nor any trace of injury caused by lava. On the contrary, on examining the perpendicular surfaces surrounding this four-sided space, every thing is ashes; 30 or 36 feet deep of ashes; only at the upper part a few bits of coal are seen, ejections from the volcano, layers corresponding with the modern eruptions, and separated by layers of vegetable earth which have had time to be deposited between the several eruptions. Look at the fragments of stuff dug out of one of those caverns—examine them—you will still find nothing in them but ashes, broken up by the pick as readily as clay or pumice.
But it may be asked, How could ashes which are light as dust, and with no coherence, gain hardness enough to take durable impressions, to form supporting arches, and to bear so delusive a look of solidity as to be taken for lava? The ready answer is found in the example of Pompeii, and the casts found in the cellars of Diomed's house; but similar and even more striking cases may help us to understand such power of adhesion. In the valleys of Monte Cavo there are ledges of peperino, formed by the filling up of volcanic ashes mingled with water. This compost grew so dense that the Romans used it for building-material. The Catacombs of Rome, which are nothing else than a volcanic tufa, that is, sand and pulverized fragments, compressed by time and their own weight, are in like manner friable, easy to cut, easier to rub down, and yet galleries are dug in them, arches, ceilings, stairways, numberless tombs, and as many as five stories of excavations, beneath each other! Nor must it be forgotten that pumice, which furnishes so excellent a water-lime, was taken originally from Pozzuola, near Vesuvius, and is nothing more than a ferruginous clay, once subjected to high volcanic temperature, and ejected in a shower of ashes. I recall, too, the great altar at Olympia, described by the traveller Pausanias, which was formed entirely from the ashes of the victims sacrificed to Jupiter. After every sacrifice the priests moistened the ashes with water from the Alpheus, smeared the altar with them, and so enlarged it gradually until, during ten centuries, the structure gained 125 feet in circuit, and 22 in height. Indeed, any one who has seen water flung into a fireplace may judge of the toughness of ashes when mixed with liquids; much more must the volcanic ashes of the Roman Campagna, of Naples and Santorin be suited for making cements.
For the rest, should this explanation only half satisfy the reader, there are the facts, and not to be denied. I defy any careful observer, examining the parts of Herculaneum hitherto brought to light, to discover any thing else in them than ashes. It may be that, on the surface of the existing soil of Portici, which has been raised at least 60 feet, marks of lava-flows are traceable which belong to modern eruptions, especially toward Resina. Neither can I affirm that, in some unexplored quarter of Herculaneum, the presence of lava may not some day be ascertained; but, as the present question is only about what we know, that is, the parts of the city which are visible, or examined already, I repeat that not the hundredth part of a square yard of lava can be found at Herculaneum, and that ashes are the only thing there is there.
The problem to be solved is, how so huge a mass of ashes was ever piled up above the unfortunate city, and, since water played so fearful a part in the catastrophe, whence that enormous quantity of water came. It is clear, in the first place, that these ashes were thrown out by the volcano. Judging from the character of the region, and from the vents formed at the mouth of the crater, the pumice-stones were all hurled toward Pompeii and Stabiæ, while the ashes drifted toward Herculaneum. Perhaps some allowance must be made for the wind which separated these substances, and the convulsions which ejected them irregularly. Then we must recollect that every very violent eruption is attended by steam produced by the sudden contact of fire with underground sheets of water. The origin of these sheets of water and the effect of their sudden gush into the furnace of eruption have been already explained. These vapors, exceeding the power of calculation in their volume and expansive force, condense at once on contact with the atmosphere; they cool, and fall again in torrents of rain. If M. Fougiré could demonstrate that in 1865, during an eruption by no means extraordinary, there fell on the mountain, in 24 hours, 22,000 cubic metres of water, the number must be multiplied by five, or even by ten, to represent that explosion of Vesuvius, a. d. 79, whose fury has never been equalled. Without adopting the hypothesis of mud-discharges from the crater, or citing the example of the volcanoes in Java, which eject mire instead of water-spouts, we may affirm that such volumes of water, mingling with the ashes and pulverized substances thrown out by other vents, suddenly produced a liquid compost, either in the air or on the ground they fell upon. The Neapolitans are familiar with a phenomenon of this sort, occurring more than once, though under limited conditions. They call it "muddy lava," and their use of the substantive would be correct if they always added the adjective, in saying that Herculaneum was buried under lava. Herculaneum, in fact, was buried by muddy lava, or, in simpler terms, by torrents of mud.
Moreover, these sudden rains, or, rather, deluges, pouring down from the sky at each outburst of steam, swept along all the ashes that had fallen on the slopes of the mountain, and carried them down upon the plain; an ash-avalanche rolled over Herculaneum. At the same time, the rivers, which ran to the right and left of the city, ceased to flow down to the sea. It has been explained how the coast was elevated, and Pliny's ships kept off, by sudden new shoals preventing access to the port of Resina. The effect of this lifting was to raise the mouths of the two rivers, and throw back their waters on the city, and this overflow added its share of mud, ashes, and vegetable matter. Nor must we omit the canals filled up, the sewers choked, the aqueducts shattered by the earthquake, and pouring their contents into the valley. By degrees, as the mud settled in the streets, the courts, rooms, and dwellings, the level of the water rose, new deposits gathered; the ashes falling in dense masses from the sky, grew saturated, and increased the rising heaps. Thus, in a few days, perhaps a few hours, a flourishing city was swallowed up, under an average thickness of sixty feet of mud. Those of the inhabitants who did not take flight at once, were drowned. In vain they climbed to the upper stories, then to the terraces and roofs—they perished at last, leaving the impressions of their bodies in the fluid ashes.
When the waters had drained away, nothing was to be seen but a grayish hillock, seamed on the surface by the streamlets which had been the last to dry up. Nothing rose above the surface, neither temple-facades, nor theatre-walls, nor tops of the loftiest buildings. Under a shell which would harden and thicken every day, Herculaneum was buried far otherwise than Pompeii had been. It was not fifteen feet of pumice stones that filled the ground floors and first stories of the houses up to the windows; it was 70 or 80 feet of compact matter that hid even the site of the city. The inhabitants who escaped must afterward have returned, as the Pompeians did; but, less fortunate, they could not revisit their homes, buried beneath their reach in unknown depths, without a trace to indicate them. Signs of excavation are thought to have been detected outside the city, above the rich villa in which the moderns have recovered 1,756 rolls of papyrus, but the owners did not dig deep enough, and their attempt was fruitless, as is proved by the art treasures discovered a century ago, which they would not have failed to carry away. It is likely that the chief impediment to digging, next to the depth, was the moisture of an alluvial deposit, in which any work soon became impossible.
But after sixteen centuries the moisture had evaporated, and the muddy lava at this day is compact and resistant enough to permit excavations in all directions throughout it. The surface has been restored to cultivation and covered with houses; Portici and Resina are populous and flourishing towns. New eruptions wrapped Herculaneum in a thicker pall, and it seemed forever blotted out from the world, until, in 1684, a baker, in digging a well, came upon ancient ruins—those of the theatre—and brought the buried city again to light.