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’.