Modern historians have made great efforts to try to understand the ancient Romans in their own terms. Though we are unlikely to come to a perfect understanding of their thinking, our attempts to reconstruct their categories will save us from crudely imposing our own ideas on them. We as Americans generally have very strong and idiosyncratic conceptions of civil war based on our one monumental war in the 19th century. Thus we need to try to understand how the ancients looked at civil war, how it was different from our view, and how this applies to the history of the empire. It should be clear that Roman experience was very different from American, so your thinking on this topic will have to begin with a survey of what could be considered civil war in Roman history, and then we can consider the following selections from ancient authors.

Lucan 1.1ff. (the beginning of an epic poem on the civil war between Caesar and Pompey composed by a poet who was censored and eventually forced to commit suicide under Nero.)

Of war I sing, war more than civil, waged over the plains of Emathia, and of legality conferred on crime; I tell how an imperial people turned their victorious right hands against their own vitals; how kindred fought against kindred; how, when the compact of tyranny was shattered, all the forces of the shaken world contended to make mankind guilty; how standards confronted hostile standards, eagles were matched against each other, and Roman javelin threatened Roman javelin.

What madness was this, my countrymen, what fierce orgy of slaughter? While the ghost of Crassus still wandered unavenged, and it was your duty to rob proud Babylon of her trophies over Italy, did you choose to give to hated nations the spectacle of Roman bloodshed, and to wage wars that could win no triumphs? Ah! with that blood shed by Roman hands how much of earth and sea might have been bought -- where the sun rises and where night hides the stars, where the South is parched with burning airs, and where the rigor of winter that no spring can thaw binds the Scythian sea with icy cold! Ere this the Chinese might have passed under our yoke, and the savage Araxes, and any nation that knows the secret of Nile's cradle. If Rome has such a lust for unlawful warfare, let her first subdue the whole earth to her sway and then commit self-slaughter; so far she has never lacked a foreign foe. But, if now in Italian cities the houses are half-demolished and the walls tottering, and the mighty stones of mouldering dwellings cumber the ground; if the houses are secured by the presence of no guard, and a mere handful of inhabitants wander over the site of ancient cities; if Italy bristles with thorn-brakes, and her soil lies unploughed year after year, and the fields call in vain for hands to till them, -- these great disasters are not due to proud Pyrrhus or the Carthagininian; no other sword has been able to wound so profoundly; deep are the strokes of a kindred hand.

Florus 2.13 (wrote a summary of Roman history in the 2nd cent. A.D.)

By this time (50 B.C.) almost all of the earth had been conquered by Rome and her empire was so great that she could not be harmed by any foreign force. But Fortune, who hated the world-ruling people, armed it for its own suicide. Indeed, the madness of Marius and Cinna had already been played out as if an experiment. The Sullan storm raged more widely, throughout Italy. But the insanity of Caesar and Pompey snatched the city, Italy, the races and peoples of the world, and all that lay in Roman jurisdiction as if by some flood or conflagration, to such an extent that it could no longer be called civil war, nor even "social," nor "external," but rather a war common to all, a more than civil war.

Fifth Century Anonymous Commentator on Lucan's first line

The war was "more than civil" quantitatively since approximately 84,000 men were slain, and qualitatively since it was fought between a father-in-law (Caesar) and a son-in-law (Pompey had married Caesar's daughter Julia).

Isidore of Seville (wrote an encyclopedia of Greco-Roman culture in the 7th century in Visigothic Spain -- he wrote in Latin)

On Wars. Ninus, the king of the Assyrians, was the first to wage war. For he was in no way content with his own borders, and therefore ruptured the natural pact of human society by leading out a hostile army, destroying others lands, and slaughtering or enslaving free peoples. He crushed into slavery all of Asia all the way to the the boundaries of Libya (sic). From him the world learned how to choke itself with its own blood.

There are four types of war: that is just, unjust, civil and more than civil. Just war is that which is fought after the enemy was warned concerning the unjust loss of holdings or for the sake of fending off enemies. Unjust war is that which is begun from wrath rather than lawful reason. Cicero speaks of this in his Republic (3,35): "Unjust wars are those begun without a reason. For there is no just reason for war outside of just vengeance or self defense." And Cicero added this shortly afterward: "No war is to be considered just unless it was openly announced and declared, unless reparation has first been demanded." Civil war involves a coup attempt and an angry disturbance arising among citizens, like that between Sulla and Marius, who waged civil war in one nation. More than civil war is when not only citizens fight, but relatives also; such as Caesar and Pompey did, when son-in-law and father-in-law fought in turn. Since indeed in this war brother fought with brother, and father carried arms against son. Cf. Lucan (2,151): "A brother falls as a brother's trophy." And also (2,150): "A son hacks the neck of his own father." Furthermore, wars are called "internal," external," "slave wars," "social wars," "pirate wars." For pirate wars are fought scattered throughout the seas... as those Pompey fought.

As that fought against enemies is called war, that which is roused by the "sedition" of citizens is called a "tumult." For a "sedition" is some strong disagreement of the citizens...However, Cicero shows how these two differ (Phil. 8,3): "It is possible for there to be a war that is not a tumult. It is not possible for there to be a tumult without a war. For what else is a tumult but a disturbance of such magnitude that immense panic breaks out?"... "a tumult is worse than a war, for in war there are lapses of hostility, whereas in a tumult there are not."

War, battle, and skirmish are all different. For the whole is called war, for instance the Punic War. The parts of war are called battles, such as Cannae. Again in one battle there are many skirmishes. For instance, one on the wings, another in the center and another on either side of the infantry. Therefore war is the whole, battle confined to one day, and skirmish is a part of the battle.