There's Tacitus's account of the Romans' attack on Mona (Anglesey). While it's highly unlikely that Tacitus was actually at the battle, he's got a reputation as a historian who was pretty serious about his sources.

By around 60CE, the Romans were doing pretty well at taking over Southern Britain, but the Welsh tribes were still giving them a lot of hassle. Suetonius Paulinus, governor of Britannia, decided to put down their resistance by taking over the island of Mona. There were probably a few reasons for this. For one thing, the Romans considered Mona to be a stronghold of the Druids, and eliminating a people's spiritual leaders is one way to make them more submissive. For another, being an island, Mona was a magnet for people fleeing Roman rule, which meant it had potential to be the cradle of an uprising. Plus it had copper mines, which the Romans wanted.

Here's Tacitus's description of the attack:

Now, however, Britain was in the hands of Suetonius Paulinus, who in military knowledge and in popular favour, which allows no one to be without a rival, vied with Corbulo, and aspired to equal the glory of the recovery of Armenia by the subjugation of Rome's enemies. He therefore prepared to attack the island of Mona which had a powerful population and was a refuge for fugitives. He built flat-bottomed vessels to cope with the shallows, and uncertain depths of the sea. Thus the infantry crossed, while the cavalry followed by fording, or, where the water was deep, swam by the side of their horses.

On the shore stood the opposing army with its dense array of armed warriors, while between the ranks dashed women, in black attire like the Furies, with hair dishevelled, waving brands. All around, the Druids, lifting up their hands to heaven, and pouring forth dreadful imprecations, scared our soldiers by the unfamiliar sight, so that, as if their limbs were paralysed, they stood motionless, and exposed to wounds. Then urged by their general's appeals and mutual encouragements not to quail before a troop of frenzied women, they bore the standards onwards, smote down all resistance, and wrapped the foe in the flames of his own brands.

Anglesey is big enough that the Druids could very easily have been somewhere other than on the battlefield if they had wanted to be. Going by Tacitus, they were there deliberately, to participate as what sounds very much like spiritual warriors.

There are definitely other examples of this, but one such was covered by /u/bitparity in this older thread so might be of itnerest!

Thanks for all the interesting sources!

SpeedBoostTorchic, The SF author Arthur Clarke wrote that "any sufficiently advanced technology is indistinguishable from magic."

So a better question to you would be: what do you mean by magic?

What do you mean by the battlefield-- hand to hand combat; or operating weapons or engines of war? Or preparing the battlefield beforehand with traps or illusions?

Is it also important they label themselves as magicians?

There's a long tradition of nearly magical engineers in Western civilization & myth-- from Daedalus, father of Icarus, to smithy gods who crafted near magical weapons of war, the crafty Odysseus who came up with the Trojan horse. We have a long paean to the wile of the mind

Sometimes magic is simply something not known to most. The Ancient Greeks knew about magnetism, for instance, and used it in temples for "magic tricks" and simple machines and they did not apply it more broadly in society; their workings remained secrets for the purposes of religious mystery.

Even now we do not know the exact things used in "Greek Fire," and Archimedes' burning mirror remains a matter of speculation of exactly what solution he used given the technology of that day. (We can easily duplicate this with modern technology), and a few other things. Even the famous Trojan Horse, we're guessing at from the clues Homer left; it was wood, it concealed men, etc.

The lack of definite records on "how" they were done is largely because deception and secrets are valuable in warfare, and they weren't going to document it precisely for their potential enemies.

In fact, many military campaigns have used some of the same principles of stage magic-- distraction, deception, illusion, secret signals overlooked by the mark, "forcing" (controlling choice made by an onlooker during a trick) and extensive preparation beforehand.

You can read up on deceptions used to deflect German forces and confuse them in advance of the Normandy Landing at D-Day. Many of them were done on the same principles as a stage illusionist would use today.

In fact, Jasper Maskelyne, a British magician of long pedigree, joined the Royal Engineers and created large illusions to fool the Germans; his efforts were so persuasive that General Wavell created the "A Force" for subterfuge and counterintelligence for Maskelyne to essentially run. This was nicknamed "the Magic Gang."

Even in Shakespeare, you see the "magic" become obvious illusion, such as the prophecy that "'Fear not, till Birnam wood Do come to Dunsinane" is regarded as impossible until MacBeth sees hidden soldiers moving onto Duninane dressed in shrubbery-- early camouflage.

And that's just the Western civilization "magic", from the Ancient Greeks on to modern illusion/stage craft. In that sense, the answer is yes, military stratagems make extensive use of the principles of magical stagecraft and always have.

Sun Tzu wrote about the value of spies in battle (Chapter 13: the Use of Spies) and the necessity of foreknowledge for military advantage. Therefore, deception is valuable in gaining advantage and weakening the opponent.

He also talked about "dead agents" (or doomed spies, depending on the translation) whose sole role was to leak misinformation to the enemy upon capture or discovery.

So you can see that deception is useful as a battle strategy, just as in magic stagecraft.

One example of forcing and distraction (cited in Polybius, III. 93, 94; Livy, XXII. 16 17) is Hannibal using a strategy apparently also used by T'ien Tan 62 years prior.

At this point, Hannibal was in hemmed-in ground as Sun Tzu would call it, among the mountains on the road to Casillinum, under attack by Fabius' forces.The Roman Dictator Fabius was using what we would call guerilla tactics today-- harassing Hannibal's much greater military, reducing their ability to forage, but always avoiding direct battle (and loss of life) and using the terrain to their advantage. It was dire.

At this point, Hannibal decided on stratagem. One night, he had bundles of twigs fastened to the horns of 2000-some oxen and set on fire. The terrified animals were quickly driven in a barely controlled stampede along the mountainside towards the enemy-controlled passes. The strange spectacle of these rapidly moving lights and the difficulty of judging distance alarmed and discomfited the Romans into withdrawing from their position, and Hannibal's army passed safely through the defile.

That's a classic magic trick right there. Blind the enemy, confuse them, force their choices in a way that you gain a safer position and can escape. And it was done by a Chinese warlord first-- T'ien Tan.

Now, these are recorded examples. There are likely many minor examples of shamans or other war leaders coming up with clever tactics to evade the enemy that were never recorded, particularly in cultures that embrace trickster-like gods/mythic figures.

Sometimes the tricks were known by everyone there but still remained unduplicated by their foes because of the long practice and skill required.

George Caitlin wrote of a trick much practiced by all Comanche warriors and riders which he said never failed to amaze him when he saw it: that when they were about to pass, they would slide over the side of their mount (which was running at full speed), effectively hidden from enemy weapons, with just his heel over the horse's back, while carrying shield, bow, and 14 foot lance, then from that position rise to shoot arrows at the foe and duck again, or with equal ease fire from under the horse's neck. Another example of a "trick" or stratagem not quickly adopted by enemies was the English use of the Welsh longbow in warfare.

The best battle secret is also often one that, after your foe sees it, and maybe even have it explained to it, they still couldn't do it, either due to their social set-up, cultural bias, or simple inability. Now, that's magically clever.

These examples might not fit your definition of magic, but they fit mine.

Now take a card, any card.