Isis disseminates videos of beheaded captives to spread simple terror. Julius Caesar knew all about it.
In his diaries of his conquest of Gaul (58–51 bc), he constantly acknowledges the power terror wielded. When it became clear, for example, that in 58 bc he would have to take on the powerful German king Ariovistus who had crossed the Rhine into Gaul, his ‘whole army was suddenly gripped by such a panic that their judgement and nerve was seriously undermined’. Caesar, naturally, rallied the troops and in the ensuing engagement drove Ariovistus’ army back across the Rhine with massive losses.
Ariovistus had been a ‘friend of Rome’. That is what Caesar did to ‘friends’ who threatened him.
In 55 bc, two other German tribes crossed the Rhine. Caesar, finding the Gauls encouraging them to roam further in Gallic territory, engaged them at once. The speed of his attack caused utter panic and confusion, and Caesar mowed down the lot, women and children too: 430,000 of them, he suggested. To press the point home, he then crossed the Rhine himself: ‘I could see the Germans were all too keen to come into Gaul, and I wanted to give them reasons to fear for their own safety…’.
Result? The terrified Germans, beaten without a fight, fled for safety deep into their heartlands.
On top of flogging enemy chieftains to death, cutting captives’ hands off, and enslaving a million or so, this was Caesar’s way: ruthless decision-making, devastating speed of assault. But knowing that Rome’s terror tactics could generate a ferocious reaction (as the British fighter Calgacus said to his troops), Caesar had other cards to play when needed — he was equally famous for his clementia. Enemies never quite knew where they were with him.
The initiative against Isis was lost as they established themselves against a useless Iraqi army. But they are not invincible, and have yet to be tested in major conflict. Caesar’s Gallic Wars would make instructive reading.