In De vita et moribus Iulii Agricolae, Tacitus describes and praises the life of his father-in-law Gnaeus Julius Agricola, an eminent Roman general. It covers briefly the people and geography of Britain, where Agricola was stationed.
Idque apud imperitos humanitas vocabatur, cum pars servitutis esset.
Because they didn't know better, they called it "civilization," when it was part of their slavery.
Variant translation: Step by step they were led to things which dispose to vice, the lounge, the bath, the elegant banquet. All this in their ignorance they called civilisation, when it was but a part of their servitude.
They plunder, they slaughter, and they steal: this they falsely name Empire, and where they make a wasteland, they call it peace.
Loeb Classical Library edition
To plunder, butcher, steal, these things they misname empire: they make a desolation and they call it peace.
As translated by William Peterson
More colloquially: They rob, kill and plunder all under the deceiving name of Roman Rule. They make a desert and call it peace.
This is a speech by the Caledonian chieftain Calgacus addressing assembled warriors about Rome's insatiable appetite for conquest and plunder. The chieftain's sentiment can be contrasted to "peace given to the world" which was frequently inscribed on Roman medals. The last part solitudinem faciunt, pacem appellant (they make a desert, and call it peace) is often quoted alone. Lord Byron for instance uses the phrase (in English) as follows,
Mark where his carnage and his conquests cease!
He makes a solitude, and calls it — peace.
Lord Byron, Bride of Abydos (1813), Canto 2, stanza 20
Et maiores vestros et posteros cogitate.
Think of your forefathers and posterity.
Proprium humani ingenii est odisse quem laeseris.
It belongs to human nature to hate those you have injured.
Chapter 42; reported in Bartlett's Familiar Quotations, 10th ed. (1919)
Tu vero felix, Agricola, non vitae tantum claritate, sed etiam opportunitate mortis.
Thou wast indeed fortunate, Agricola, not only in the splendour of thy life, but in the opportune moment of thy death. 
The Germans themselves I should regard as aboriginal, and not mixed at all with other races through immigration or intercourse. For in former times, it was not by land but on shipboard that those who sought to emigrate would arrive; and the boundless and, so to speak, hostile ocean beyond us,is seldom entered by a sail from our world.
They even say that an altar dedicated to Ulysses, with the addition of the name of his father, Laertes, was formerly discovered on the same spot, and that certain monuments and tombs with Greek inscriptions, still exist on the borders of Germany and Rhaetia.
On the whole,one would say that their strength is in their infantry, which fights along with the cavalry; admirably adapted to the action of the latter is the swiftness of certain foot soldiers, who are picked from the entire youth of their country, and stationed in front of the line.
Scutum reliquisse praecipuum flagitium, nec aut sacris adesse aut concilium inire ignominioso fas; multique superstites bellorum infamiam laqueo finierunt.
To abandon your shield is the basest of crimes; nor may a man thus disgraced be present at the sacred rites, or enter their council; many, indeed, after escaping from battle, have ended their infamy with the halter.
Mercury is the deity whom they chiefly worship, and on certain days they deem it right to sacrifice to him even with human victims.
Quanquam severa illic matrimonia
However the marriage is there severe.
Start of chapter 18
This is in the sense that the matrimonial bond was strictly observed by the Germanic peoples, this being compared favorably against licentiousness in Rome. Tacitus appears to hold the fairly strict monogamy (with some exceptions among nobles who marry again) between Germanic husbands and wives, and the chastity among the unmarried to be worthy of the highest praise. (Ch. 18).
…ibi boni mores valent quam alibi bonae leges. 
…good habits are here more effectual than good laws elsewhere. 
End of chapter 19
No one in Germany laughs at vice, nor do they call it the fashion to corrupt and to be corrupted.
Indeed, the crowning proof of their valour and their strength is that they keep up their superiority without harm to others.
Their shields are black, their bodies dyed. They choose dark nights for battle, and, by the dread and gloomy aspect of their death-like host, strike terror into the foe, who can never confront their strange and almost infernal appearance.
All this is unauthenticated, and I shall leave it open.
Rara temporum felicitate, ubi sentire quae velis, et quae sentias dicere licet.
Translation: It is the rare fortune of these days that one may think what one likes and say what one thinks.
Book I, 1
Once killing starts, it is difficult to draw the line.
Book I, 39
He possessed a peculiar talent of producing effect in whatever he said or did.
Book II, 80
Expugnatae urbis praedam ad militem, deditae ad duces pertinere.
The soldiers have the plunder of a city that is stormed, the generals of one which capitulates.
Book III, 19; Church-Brodribb translation
Divisa inter exercitum ducesque munia: militibus cupidinem pugnandi convenire, duces providendo, consultando, cunctatione saepius quam temeritate prodesse. ut pro virili portione armis ac manu victoriam iuverit, ratione et consilio, propriis ducis artibus, profuturum.
There is a division of duties between the army and its generals. Eagerness for battle becomes the soldiers, but generals serve the cause by forethought, by counsel, by delay oftener than by temerity. As I promoted your victory to the utmost of my power by my sword and by my personal exertions, so now I must help you by prudence and by counsel, the qualities which belong peculiarly to a general.
Book III, 20; Church-Brodribb translation
Some might consider him as too fond of fame; for the desire for glory clings even to the best men longer than any other passion.
So obscure are the greatest events, as some take for granted any hearsay, whatever its source, others turn truth into falsehood, and both errors find encouragement with posterity.
Tiberii Gaique et Claudii ac Neronis res florentibus ipsis ob metum falsae, postquam occiderant, recentibus odiis compositae sunt. inde consilium mihi pauca de Augusto et extrema tradere, mox Tiberii principatum et cetera, sine ira et studio, quorum causas procul habeo.
The histories of Tiberius, Caius, Claudius, and Nero, while they were in power, were falsified through terror, and after their death were written under the irritation of a recent hatred. Hence my purpose is to relate a few facts about Augustus - more particularly his last acts, then the reign of Tiberius, and all which follows, without either bitterness or partiality, from any motives to which I am far removed.
Book I, 1; Church-Brodribb translation
Pacem sine dubio post haec, verum cruentam.
No doubt, there was peace after all this, but it was a peace stained with blood.
Book I, 10; Church-Brodribb translation
Nihil deorum honoribus relictum, cum se templis et effigie numinum per flamines et sacerdotes coli vellet.
No honour was left for the gods, when Augustus chose to be himself worshipped with temples and statues, like those of the deities, and with flamens and priests.
Book I, 10; Church-Brodribb translation
Ne Tiberium quidem caritate aut rei publicae cura successorem adscitum, sed quoniam adrogantiam saevitiamque eius introspexerit, comparatione deterrima sibi gloriam quaesivisse.
He had not even adopted Tiberius as his successor out of affection or any regard to the State, but, having thoroughly seen his arrogant and savage temper, he had sought glory for himself by a contrast of extreme wickedness.
Book I, 10; Church-Brodribb translation
So true is it that all transactions of preeminent importance are wrapt in doubt and obscurity; while some hold for certain facts the most precarious hearsays, others turn facts into falsehood; and both are exaggerated by posterity.
Book III, 19
Variant: So obscure are the greatest events, as some take for granted any hearsay, whatever its source, others turn truth into falsehood, and both errors find encouragement with posterity.
And now bills were passed, not only for national objects but for individual cases, and laws were most numerous when the commonwealth was most corrupt.
Viginti clarissimarum familiarum imagines antelatae sunt, Manlii, Quinctii aliaque eiusdem nobilitatis nomina. sed praefulgebant Cassius atque Brutus eo ipso quod effigies eorum non visebantur.
The busts of twenty most illustrious families were borne in the procession, with the names of Manlius, Quinctius, and others of equal rank. But Cassius and Brutus outshone them all, from the very fact that their likenesses were not to be seen.
This line is the origin of Lord John Russell's phrase "Conspicuous by its absence"; of which Russell said "It is not an original expression of mine, but is taken from one of the greatest historians of antiquity". Similar phrases also are found in the tragedy Tiberius of Joseph Chénier and in Les Hommes Illustres of Charles Perrault.
Punitis ingeniis, gliscit auctoritas.
When men of talents are punished, authority is strengthened.
Book IV, 35.
He had talents equal to business, and aspired no higher.
Book VI, 39
He upbraided Macro, in no obscure and indirect terms, "with forsaking the setting sun and turning to the rising".
Book VI, 52, referring to Tiberius
What is today supported by precedents will hereafter become a precedent.
Book XI, 24
Habet aliquid ex iniquo omne magnum exemplum, quod contra singulos, utilitate publica rependitus.
Every great example of punishment has in it some injustice, but the suffering individual is compensated by the public good.
Book XIV, 44
nisi impunitatis cupido retinuisset, magnis semper conatibus adversa.
The desire for safety stands against every great and noble enterprise.
Book XV, 50, in his account of Subrius Flavus’ passing thought of assassinating Nero while the emperor sang on stage.
Variant translation: "but desire of escape, foe to all great enterprises, held him back."
cupido dominandi cunctis adfectibus flagrantior est
Lust of absolute power is more burning than all the passions