16I have explained what I thought most requisite respecting scorpions, catapultæ, balistæ, no less than tortoises and towers, who invented them, and in what manner they ought to be made. It did not seem necessary to write on ladders, cranes, and other things of simpler construction; these the soldiers of themselves easily make. Neither are they useful in all places, nor of the same proportions, inasmuch as the defences and fortifications of different cities are not similar: for machines constructed to assault the bold and impetuous, should be differently contrived to those for attacking the crafty, and still dissimilar, where the parties are timid.
2Whoever, therefore, attends to these precepts, will be able to select from the variety mentioned, and design safely, without further aid, such new schemes as the nature of the places and other circumstances may require. For the defence of a place or army, one cannot give precepts in writing, since the machines which the enemy prepares may not be in consonance with our rules; whence oftentimes their contrivances are foiled by some ready ingenious plan, without the assistance of machines, as was the case with the Rhodians.
3Diognetus was a Rhodian architect, who, to his honour, on account of his great skill, had an annual fixed salary. At that period, an architect of Aradus, whose name was Callias, came to Rhodes, obtained an audience, and exhibited a model of a wall, whereon was a revolving crane, by means whereof he could suspend an Helepolis near the spot, and swing it within the walls. The wondering Rhodians, when they saw it, took away the salary from Diognetus, and conferred it on Callias.
4Immediately after this, king Demetrius, who, from his resolution, was sirnamed Poliorcetes, prepared to wage war against the Rhodians, and brought in his train Epimachus, a celebrated architect of Athens. This person prepared an helepolis of prodigious expense and of ingenious and laborious construction, whose height was one hundred and twenty-five feet, and its width sixty feet: he secured it, moreover, with hair-cloths and raw hides, so that it might securely withstand the shock of a stone of three hundred and sixty pounds weight, thrown from a balista. The whole machine weighed three hundred and sixty thousand pounds. Callias being now requested by the Rhodians to prepare his machine against the helepolis, and to swing it within the wall, as he had promised, confessed he was unable.
5For the same principles do not answer in all cases. In some machines the principles are of equal effect on a large and on a small scale; others cannot be judged of by models. Some there are whose effects in models seem to approach the truth, but vanish when executed on a larger scale, as we have just seen. With an auger, a hole of half an inch, of an inch, or even an inch and a half, may be easily bored; but by the same instrument it would be impossible to bore one of a palm in diameter; and no one would think of attempting in this way to bore one of half a foot, or larger.
6Thus that which may be effected on a small or a moderately large scale, cannot be executed beyond certain limits of size. When the Rhodians perceived their error, and how shamefully they had wronged Diognetus; when, also, they perceived the enemy was determined to invest them, and the machine approaching to assault the city, fearing the miseries of slavery and the sacking of the city, they humbled themselves before Diognetus, and requested his aid in behalf of his country.
7He at first refused to listen to their entreaties; but when afterwards the comely virgins and youths, accompanied by the priests, came to solicit his aid, he consented, on condition that if he succeeded in taking the machine, it should be his own property. This being agreed to, he ordered a hole to be made in that part of the wall opposite to the machine, and gave general as well as particular notices to the inhabitants, to throw on the other side of the hole, through channels made for the purpose, all the water, filth, and mud, that could be procured. These being, during the night, discharged through the hole in great abundance, on the following day, when the helepolis was advanced towards the wall, it sunk in the quagmire thus created: and Demetrius, finding himself overreached by the sagacity of Diognetus, drew off his army.
8The Rhodians, freed from war by the ingenuity of Diognetus, gave him thanks publicly, and loaded him with honours and ornaments of distinction. Diognetus afterwards removed the helepolis within the walls, placed it in a public situation, and inscribed it thus: “Diognetus presented this to the people out of the spoils of war.” Hence, in defensive operations, ingenuity is of more avail than machines.
9A similar circumstance occurred at Chios, where the enemy had got ready sambucæ on board their ships; the Chians, during the night, threw into the sea, at the foot of their wall, earth, sand, and stones; so that when the enemy, on the following day, endeavoured to approach it, the ships got aground on the heaps thus created under water, without being able to approach the wall or to recede; in which situation they were assailed with lighted missiles, and burnt. When, also, the city of Apollonia was besieged, and the enemy was in hopes, by undermining, to penetrate into the fortress unperceived; the spies communicated this intelligence to the Apollonians, who were dismayed, and, through fear, knew not how to act, because they were not aware at what time, nor in what precise spot, the enemy would make his appearance.
10Trypho, of Alexandria, who was the architect to the city, made several excavations within the wall, and, digging through, advanced an arrow’s flight beyond the walls. In these excavations he suspended brazen vessels. In one of them, near the place where the enemy was forming his mine, the brazen vessels began to ring, from the blows of the mining tools which were working. From this he found the direction in which they were endeavouring to penetrate, and then prepared vessels of boiling water and pitch, human dung, and heated sand, for the purpose of pouring on their heads. In the night he bored a great many holes, through which he suddenly poured the mixture, and destroyed those of the enemy that were engaged in this operation.
11Similarly when Marseilles was besieged, and the enemy had made more than thirty mines; the Marseillois suspecting it, lowered the depth of the ditch which encompassed the wall, so that the apertures of all the mines were discovered. In those places, however, where there is not a ditch, they excavate a large space within the walls, of great length and breadth, opposite to the direction of the mine, which they fill with water from wells and from the sea; so that when the mouths of the mine open to the city, the water rushes in with great violence, and throws down the struts, overwhelming all those within it with the quantity of water introduced, and the falling in of the mine.
12When a rampart composed of the trunks of trees is raised opposite to a wall, it may be consumed by discharging red hot iron bars against it from the balistæ. When, also, a tortoise is brought up to batter a wall with a ram, a rope with a noose in it may be lowered to lay hold of the ram, which being then raised by means of a wheel and axle above, keeps the head suspended, so that it cannot be worked against the wall: lastly, with burning arrows, and with discharges from the balistæ, the whole machine may be destroyed. Thus all these cities are saved and preserve their freedom, not by machines, but by expedients which are suggested through the ready ingenuity of their architects. I have, in this book, to the best of my ability, described the construction of those machines most useful in peace and war. In the preceding nine I treated of the other branches of Architecture, so that the whole subject is contained in ten books.