The arsenal and clothing of the man accused of killing 50 people in attacks on two New Zealand mosques was covered in symbols and writing. Some were references to Adolf Hitler; elsewhere, he invoked the names of other mass shooters.

But many of the more obscure references were clear to medieval historians. It’s a pattern they have seen repeated by white supremacists, white nationalists and neo-Nazis again and again in recent years — at Charlottesville’s deadly Unite the Right rally, at a conference sponsored by alt-right leader Richard Spencer, and by the man in Portland, Ore., who allegedly killed two people after harassing a woman wearing hijab.

“They’re using their messed-up concept of the Middle Ages as a recruitment tool, and that’s a huge problem,” says Paul B. Sturtevant, author of “The Middle Ages in Popular Imagination” and editor in chief of the Public Medievalist.

Sturtevant counted 18 references to the Middle Ages in the markings and writing on the arsenal that belonged to Brenton Harrison Tarrant, the 28-year-old Australian charged in Friday’s New Zealand rampage.