The military readers of this site might be especially interested in this older look at potential counter-insurgency strategy. I've certainly found it to be quite perceptive based on my experience.
From the 'Discourses'
CHAPTER XXIVFORTRESSES ARE GENERALLY MORE HARMFUL THAN USEFUL
It may perhaps appear to these sages of our times as something not well considered, that the Romans in wanting to assure themselves of the people of Latium and of the City of Privernum, did not think of building some fortresses there, which would be a restraint to hold them faithful; especially as there was a saying in Florence alleged by our wise men, that Pisa and other similar Cities ought to be held by fortresses. And truly, if the Romans had been like them, they would have thought to build them: but as they were of another virtu, of another judgment, of another power, they did not build them. And so long as Rome lived free and followed her institutions and virtuous constitutions, they never built one to hold either a City or a province, but they did save some that had already been built. Whence seeing the mode of proceeding of the Romans in this regard, and that of the Princes in our times, it appears to me proper to put into consideration whether it is good to build fortresses, or whether they are harmful Or useful to him who builds them. It ought to be considered, therefore, whether fortresses are built for defending oneself from the enemy or to defend oneself form one’s subjects.
In the first case they are not necessary, in the second harmful. And I will begin by giving the reason why in the second case they are harmful, I say that that Prince or that Republic which is afraid of its subjects and of their rebelling, it results first from the fact that that fear arises from the hate which the subjects have for them, and the hate they have of the treatment given them. The ill treatment results either from the belief of being able to hold them by force, or from the little prudence of those who govern them; and one of the things that makes them believe they are able to force them, is to have their fortresses near them: for the ill treatment that is the cause of hatred, arises in good part because of that Prince or that Republic have the fortresses, which (if this is true) are much more harmful by far than useful: For firstly (as has been said) they cause you to be more audacious and more violent toward your subjects: afterwards there is not that internal security of which you persuade yourself, as all the strength and violence that is employed in holding a people are nothing, except these two: either you have always to place a good army in the field, as the Romans had, or you must disperse them, extinguish them, disorganize them, and so destroy them that they are not able to come together to attack you; for if you impoverish them, the despoiled ones will win their arms: if you disarm them, fury will serve as arms: if you kill the Captains and continue to injure the others, the Heads will spring up as those of the Hydra: if you build fortresses, they are useful in times of peace because they give you more courage to do evil to them, but in times of war most useless because they will be assaulted by the enemy and by your subjects, nor is it possible that they can resist the one and the other. And if ever they were useless, they are now in our times on account of artillery, because of which the small places, where moreover you cannot retire behind earthworks, are impossible to defend, as we discussed above.
I want to discuss this manner more tritely. Either you, a Prince, want to keep the people of the City in restraint with these fortresses, or you, a Prince or a Republic, want to keep a City in restraint that has been occupied in war. I want to turn to the Prince, and I say to him that such fortresses cannot be more useless to him in holding his Citizens in restraint for the reasons given above, for it makes you more prompt and less regardful in oppressing them, and that oppression will expose you to your ruin and will excite them so, that that fortress which is the reason for it cannot afterwards defend you; so that a wise and good Prince, in order to keep himself good and not give cause to his sons to dare to become bad, will never build fortresses, so that they will rely, not upon the fortresses, but on the good will of men. And if Count Francesco Sforza who had become Duke of Milan was reputed wise and none the less built fortresses in Milan, I say that in this case he was not wise, and the result has shown that that fortress was harmful and not a security to his heirs: for judging that through the medium of it to live securely, and to be able to oppress their Citizens and subjects, they indulged in all kinds of violence, so that they became so hated as described above, that they lost the State as soon as the enemy assaulted them: nor did that fortress defend them, nor did they have any usefulness for them in war, and in peace had done them much harm: for if they had not had them, and if because of little prudence they had not treated their Citizens harshly, they would have discovered the peril more quickly, and would have retreated, and would then have been able to resist the impetus of the French more courageously with friendly subjects and without a fortress, than with hostile subjects, and with the fortress, which do you no good in any way, for either they [fortresses] are lost through the treachery of those who guard them, or because of the violence of those who assault it, or by famine.
And if you want them to do you any good and to help you in recovering a lost State, where only the fortress remains to you, it behooves you to have an army with which you can assault those who have driven you out; and if you have the army you would recover the State in any case, [and] even more [easily] if the fortress did not exist, and so much more easily as men would be more friendly than they were to you, for you had maltreated them because of the pride of having the fortress. And from experience it has been seen that this fortress of Milan was of no usefulness either to the Sforza or to the French in times of adversity for the one or the other; rather it brought much harm and ruin to both, not having given thought because of it to more honest means of holding that State. Guidobaldo Duke of Urbino, son of Frederick, who is his time was an esteemed Captain, was driven out of his State by Cesare Borgia, son of Pope Alexander VI; when afterwards because of an incident that had arisen he returned there, he caused all the fortresses that existed in that province to be destroyed, judging them to be injurious. For he being beloved by men, did not need them on their account, and with regard to his enemies, he had seen that he could not defend them; as they needed an army in the field to defend them, he resolved to destroy them. Pope Julius, after having driven out the Bentivogli from Bologna, built a fortress in that City, and afterwards had those people assassinated by one his Governors: so that that people rebelled, and the Pope quickly lost the fortress; and thus the fortress did him no good, but injury, and the more so, that by conducting himself otherwise it could have done him good. Niccolo Da Costello, father of the Vitelli, returning to his country when he had been exiled, quickly razed two fortresses that Pope Sixtus IV had built, judging that the good will people, not the fortresses, would keep him in that State. But of all the other examples, the most recent and the most notable in every way, and apt to show the uselessness of building them and the usefulness of destroying them, is that of Genoa which ensued in the most recent time. Everyone knows that in MDVII [1507] Genoa rebelled against Louis XII, King of France, who had come in person with all his forces to recover it, and having recovered it, he had a fortress built stronger than all others known up to the present time; it was impregnable because of its location and other circumstances, being placed on the apex of a hill that extended into the sea, called Codefa by the Genoese, and by means of this he commanded all the port and great part of the town of Genoa. Afterwards in the year MDVII [1512] it happened that the French forces were driven out of Italy, Genoa rebelled notwithstanding the fortress, and Ottaviano Fregoso seized the State, who, after sixteen months and with every industry, captured it by starvation. And everyone believed, and many counselled him, that he should preserve it as a refuge in any event: but being a most prudent man, [and] knowing that the good will of men and not fortresses maintained Princes in their States, destroyed it. And thus without founding his State on the fortress, but on his virtu and prudence, he has held it and still holds it. And where before only a thousand infantry usually were enough to overturn the State of Genoa, his adversaries have assaulted him with ten thousand and have not been able to harm him. It will be seen from this, therefore, that the destruction of the fortress did no more harm Ottaviano, than the building of it protected the King of France. For when he was able to come into Italy with his army, he was able to recover Genoa without the fortress being there; but without the army he could not come into Genoa even though he had a fortress there. For him, therefore, it was an expense to do [build] it and a disgrace to lose it: To Ottaviano the recovery of it was glorious and the destruction of it useful.
But let us come to the Republics which build fortresses, not within their own country, but inside the towns they acquire. And if the example given of France and Genoa are not enough to demonstrate the fallacy of this, those of Florence and Pisa will be enough for me; for the Florentines build fortresses in order to hold that City, and did not understand that to hold a City which was always hostile to Florentine rule, had lived in freedom, and had resorted to rebellion as a refuge for liberty, it was necessary in wanting to observe the old Roman method, either to make her an associate or to destroy her: for the virtu of fortresses is seen in the coming of King Charles, to whom they all surrendered, either through the treachery of those who guarded it, or from fear of a greater evil: for if there had not been one, the Florentines never would have based their holding Pisa on it, and the King [of France] could never in that manner have deprived the Florentines of that City: and the means by which they had maintained it up to that time would perhaps have been sufficient to preserve it, and without doubt would have stood the test better than the fortress.
I conclude, therefore, that to hold one’s own country a fortress is injurious and to hold towns that are acquired fortresses are useless: And I want the authority of the Romans to be enough [for me], who razed the walls of those towns which they wanted to hold, having taken them by violent means, and never rebuilt them. And if anyone should cite in opposition to this opinion that [example] of Tarantum in ancient times and of Brescia in modern times, both of which places were recovered from their rebellious subjects by means of fortresses, I reply, that for the recovery of Tarantum Fabius Maximus was sent at the beginning of the year with the entire army, who would have been more apt to have recovered it if there had not been a fortress: for although Fabius had used that means, if there had not been this means [fortress], he would have used other means which would have had the same result. And I do not know of what usefulness a fortress may be, if in the recovery of a town, a consular army with Fabius Maximus for its Captain is needed to recover it: And that the Romans would have recovered it in any event, is seen by the example of Capua where there was no fortress, and which they reacquired through the virtu of the army. But let us come to Brescia. I say that there rarely occurs that which occurred in that rebellion, that while the fortress remains in your power (the town having revolted) you should have a large army [and] nearby as was that of the French: for Monsignor De Foix, Captain of the King, being with his army at Bologna and learning of the loss of Brescia recovered the town by means of the fortress. The fortress of Brescia, therefore, (in order to be of benefit) also needed a Monsignor De Foix, and a French army which had to succor it in three days: Hence this example in contrast to opposite examples is not enough, for many fortresses have been taken and retaken in wars of our times, by the same fortune as field campaigns [have taken and retaken], not only in Lombardy, but also in the Romagna, in the Kingdom of Naples, and throughout all parts of Italy.
But as to building fortresses in order to defend oneself from external enemies, I say that they are not necessary to those people, or to those Kingdoms that have good armies, and are useless to those who do not have good armies: for good armies without fortresses are sufficient to defend themselves, and fortresses without good armies cannot defend you. And this is seen from the experience of those who are held to be excellent as governors and in other things, as was the case with the Romans and the Spartans; for if the Romans did not build fortresses, the Spartans not only abstained from building them, but even did not permit the City to have walls, because they wanted [to rely on] the personal virtu of their men to defend them, [and] not some other means of defense. When, therefore, a Spartan was asked by an Athenian whether the walls of Athens appeared beautiful to him, he replied “yes, if the [City] was inhabited by women”.
The Prince, therefore, who has good armies, may have on the frontiers of his State, or on the sea, some fortresses that could resist the enemy for some days until he could be checked; this may sometimes be a useful thing, but is not a necessary one. But when the Prince does not have a good army, then having fortresses throughout his State or at the frontiers, are either injurious or useless to him: injurious, because he loses them easily, and when they have been lost they are turned [make war] against him; or even if they should be so strong that that enemy cannot occupy them, they are left behind by the enemy army, and are of no benefit; for good armies, unless they are confronted by equally brave ones, enter into enemy country regardless of the City or fortress which they leave behind, as is seen in ancient histories; and as Francesco Maria did, who in recent times, in order to assault Urbino, left ten enemy Cities behind him, without taking any account of them. That Prince, therefore, who can raise a good army, can do without building fortresses: He who does not have a good army, ought not to build. He ought indeed to fortify the City where he lives, and keep it fortified, and keep the Citizens of that City well disposed, in order to be able to sustain an enemy attack so that he can [keep it] free by an accord or by external aid. All other plans are an expense in times of peace, and useless in times of war. And thus whoever considers all that I have said, will recognize the Romans as wise in all their other institutions, as they were prudent in their judgments concerning the Latins and the Privernati, where, not thinking of fortresses, they assured themselves of these people by wiser and more virtuous means.
