§ 1. Armies cross rivers in four ways: by bridge, by boat, by diverting the river into channels, and by swimming. For if it is possible to cross by a ford, there is no need of a new art. Then attention must be given only to this: that the enemy has not obstructed a slender stream by night so that, when the water swells, it is no longer passable. The Dutch garrison did this in the siege of Ostend. There is another danger if they cast down caltrops, which easily escape notice when the water has been disturbed.
§ 2. There is therefore severe difficulty at rivers. Vegetius, book 3, chapter 7. It is difficult, I say, when the enemy is nearby, for making a bridge is a greater labor. Boats are easily driven back by cannon and fixed stakes; today it is scarcely possible to cross by swimming, although under Charles V certain Spaniards swam across the Elbe. But the enemy’s panic gave them their opportunity, for if even five cavalrymen had been on the bank, they could have repelled those approaching.
§ 3. The entire art therefore consists in pretending that one will cross in one place and crossing in another. When crossing a river, Labienus made a noise with oars in one place, so that he might appear to be crossing there; while the enemy prepared himself, Labienus crossed in another place. Sinan Pasha also did this in the year 1594. For after pretending that he would cross the Danube in several places, he crossed at one place distant from the Christian camp and at the same time carried off part of their baggage.
The Tatars crossed the Danube with utter foolishness in the year 1596, holding the tail of a horse with one hand and a sword with the other; but they were cut down when they had crossed. That method is dangerous, because horses are easily burdened, and if they perceive danger, they kick.
§ 4. They were accustomed to check the current of a river with horses or elephants. Caesar positioned cavalry above and below, so that they would break the river’s current, in book 1 of The Civil War: “He leads out the remaining legions without baggage and, after stationing a great number of pack animals in the river above and below, leads the army across.” Hannibal positioned elephants in the Po.
§ 5. Ice must be crossed cautiously. Scatter straw upon it and pour water over it so that it freezes, lest the pack animals or soldiers fall upon the slippery surface. Julius II crossed the Po in this way.
The Tatars were afraid to cross the frozen Danube. They therefore left a multitude of cattle together with their tents and withdrew as though afraid. The Hungarians who were on the opposite side drove the herds across. When the Tatars learned this and understood that an army could cross, they followed and devastated Hungary. Fulgosus, book 7.
§ 6. Datames joined carts to carts and affixed boards to the rims, so that they would not sink too deeply into the mud. He had ordered the strongest men to swim across together with the pack animals; these men drew the carts, and in this manner he led the army across. Rafts can nevertheless be joined together by an easier method.
To destroy bridges men are accustomed to send fire-ships against them. At present there is the greatest opportunity for this. They employed that art admirably at Antwerp; nor, when two attempts had failed, did they desist. The third caused immense loss.
§ 7. Because it is exceedingly difficult to cross rivers, very many stratagems have been devised for that labor. While the Pisidian inhabitants guarded the narrow places, Autophradates began to prepare a crossing elsewhere. When they went to meet him, he occupied the narrow places by night and led his army across.
Pompey repeatedly led his army out and brought it back into camp. When this had been done and the enemy thought that he was being mocked, he became negligent, and Pompey crossed by a sudden movement. Alexander and Xenophon, pretending to cross in one place, crossed in another.
By an amusing stratagem the Laconians sailed through a Carthaginian fleet stationed in their way and reached Syracuse. They had ten captured Punic ships; they caused these to be led first as if victorious, with the other ships joined to their sides and fastened to their sterns. By this appearance they deceived the Carthaginians and passed through.
The crossing of Sertorius was laborious. He drew a rampart in the form of a hollow crescent, filled it with material, and set it on fire, and in this way shut out the enemy. But much material was needed, lest the enemy attack when the fires were scattered. Today they can be kept away more easily because of the danger that gunpowder will catch fire. Pelopidas the Theban also did the same, as did Herculeius, the lieutenant of Sertorius, between two mountains.
Hanno, when shut in, heaped up light materials in a place suitable for breaking out and set them on fire. After the enemy had been called away to the other exits, he went out through the flames, the soldiers’ faces protected by shields and their legs by cloth.
When the enemy occupied the bank of a river and Quintus Lutatius Catulus could not cross, he pretended that he was about to establish a camp. The Cimbri believed this to be true and did the same themselves. When they had gone out to gather wood and forage, Catulus crossed and attacked their camp.
When Croesus could not cross the Halys, he drew a ditch behind the army and diverted the river into it.
§ 8. Necessity often discovers many devices. When Metellus lacked ships for transporting elephants into Sicily, he joined barrels together and covered them with platforms. Hannibal ordered a soldier to wound an elephant beneath the ear and then to swim across the river. The beast, eager for revenge, followed him and gave the rest an example of daring the same thing. Otherwise the elephants could not be compelled by any force to cross.
§ 9. This principle is general: they should break in where they are not expected. Yet the industry of Scipio in this matter is both excellent and necessary. At Carthage he broke in by following the tide of the sea, declaring that he was following God as his guide.
Take an example from other actions in order to cross rivers, for whatever is done on land is less difficult than what is accomplished through the waves. Marius sent soldiers into a fortress over a rugged mountain. You will make the attempt through whirlpools. When Joshua had placed an ambush beside the city of Ai and the soldiers fled, he occupied the city through those who had been placed in ambush. Lucius Cornelius imitated this in many towns in Sardinia; Cato among the Lacetani; Lucius Scipio in Sardinia; Hannibal at Himera and Saguntum; Himilco at Agrigentum; Viriathus at Segobriga; Barca at Lilybaeum; and the Scordisci at Heraclea.
They sound the alarm in one part and attack in another. In this way Alcibiades occupied Cyzicus, Pericles a fortress of the Peloponnesians, Thrasybulus Miletus, and Antiochus Ephesus. Rivers, harbors, and marshes all furnish both greater necessity and greater opportunity.
Some made bundles of reeds and sedge in order that cavalrymen might place their arms upon them while they themselves crossed by swimming. Appian, book 8, writes concerning barrels: “But there was a great scarcity of timber and vessels with which, by joining them together, a bridge might be made. Certain workmen reported that there were very many empty, round barrels in the deserted fields there, which the inhabitants had formerly used for importing wine. Since these were hollow in the likeness of ships, when bound to one another they seemed likely to float after the manner of small boats. Indeed, once fastened together with bindings, with wickerwork laid over them and a great deal of earth heaped upon them, they could not sink. When this had been done, the soldiers easily crossed to the farther bank.”
Lucan likewise, book 4:
New devices for flight across the waters are sought out. They do not extend keels in the customary manner and raise sterns; instead they bind stout timbers, capable of bearing great weights, in an unfamiliar construction. For empty barrels sustain a raft on every side; their row, bound with chains stretched at length, receives slanting alders in two ranks.
They also made bridges from inflated skins, lest the army’s necessary march should sometimes be impeded by the courses of rivers, as very often happens. Resourceful necessity discovered a remedy for this matter which is both easy to make and of outstanding utility. It is constructed in the following manner.
Calfskins are softened by the Arabian art, for among the Arabs particular care is given to their preparation because water must be drawn from wells in skins. These, then, are carefully sewn as has been said, so that the structure is three and one-half feet in size. Thus, when the same skins have been inflated with air and swollen, they do not raise up a belly; rather, by a certain evenness, the very fullness of the skins produces level surfaces. They are bound to one another at their sides by straps fastened underneath. Rings project above them on one side, and hooks are inserted on the other. Thus the complete structure, joined part to part in the form of a bridge, is unfolded.
The same work, however, will be extended more easily aslant across the river to the opposite bank on account of the force of the current. Iron stakes are fixed on each bank, and strong ropes are stretched in the middle beneath the skins themselves to sustain the weight of those walking and above the edges for stability. By this novel and foreign preparation for a road, it will within a short space of time furnish a free opportunity to cross the river.
We must further be advised that coarse cloths should be spread over the joined skins beneath the feet of those walking, lest the smooth dressing of the hides deny them a firm footing. Nevertheless, hand-ballistae will be positioned on both banks, lest an enemy force hinder those working upon the bridge.
In the Mithridatic War Lucullus saved Cyzicus in this way. Florus, book 3: “But a messenger gave the townsmen confidence to resist by teaching them that Lucullus was approaching. Horrible to tell, he passed through the midst of the enemy’s ships suspended from an inflated skin and guiding his course with his feet. To those watching from a distance he escaped like a sea-monster.” Indeed, Gaius Caesar too, supported by inflated skins, often outran the messengers concerning himself.
Caesar says in book 1 of The Civil War that the Lusitanians did not go to war without inflated skins; and Livy, book 30, says the same of the Spaniards, who also placed their clothing in the skins. Others used shields. The Lycians secretly returned to their city by swimming underwater through the Xanthus; Brutus caught them in nets.
A safer method is to make dugout canoes, or small boats from one piece of wood. Caesar used these in Britain, and in Spain; Livy, book 30; Ammianus, books 14 and 24. They also carried skiffs with them. Julian did so in Persia, Ammianus, book 14. Semiramis had boats that could be taken apart and carried them upon camels. Diodorus, book 3. The emperor Alexander also laid a bridge upon dugout canoes when he crossed the Rhine. Caesar made ships against Sextus Pompey from wickerwork of willow and ox hides.
Battles very often arise at a crossing. Caesar, book 2 of The Gallic War: “The fighting in that place was fierce. Our men attacked the enemy while they were encumbered in the river and killed a great number of them. By a multitude of missiles they drove back the remainder, who attempted with the greatest boldness to cross over the bodies of their men. They surrounded with cavalry and killed the first who had crossed.”
The ancients also drove off the enemy by ingenuity. Diodorus, book 19:
παρασκευασάμενοι γὰρ δέσμους καλάμων εὐμεγέθεις ἐμβάλλουσιν εἰς τὴν λίμνην· ἐπὶ δὲ τούτων ἐπικάθηνται οὐ πλείω τριῶν, ὧν δύο μὲν ἔχοντες προσδεδεμένας πλάτας κωπηλατοῦσιν, εἷς δὲ φορῶν τόξα τοὺς προσπλέοντας ἐκ τοῦ πέραν ἢ βιάζεσθαι τολμῶντας ἀμύνεται.
For after preparing large bundles of reeds they cast them into the lake. Upon these no more than three men take their seats: two, holding blades fastened to them, row, while one, carrying a bow, wards off those sailing against them from the opposite side or daring to use force.
The Liburnians acted bravely and amusingly when they occupied shallow places with only their heads projecting. They caused the enemy to believe that the sea was deep; and when a trireme pursuing them became entangled in the shallows, they captured it.
Men are accustomed to obstruct harbors and the mouths of rivers. Our countrymen have learned to obstruct a crossing in every manner. At Hamburg Duke Valdemar of Schleswig obstructed the Elbe with chains; at Danzig Stephen, king of Poland, obstructed it with a bridge. But here the river and the surrounding places must be considered.