Albert of Aix, a Christian born in the late 11th century, describes atrocities in Mainz — another stop on the crusaders’ rampage through the Rhineland — by a band headed by one Count Emico. Again, there is a bishop who initially promises the Jews protection for what Albert describes as an “incredible amount of money.” But Emico and his Christian soldiers broke into the hall where the Jews were held.

“Breaking the bolts and doors, they killed the Jews, about seven hundred in number, who in vain resisted the force and attack of so many thousands. They killed the women, also, and with their swords pierced tender children of whatever age and sex ... Horrible to say, mothers cut the throats of nursing children with knives and stabbed others, preferring them to perish thus by their own hands rather than to be killed by the weapons of the uncircumcised.”

Albert reports that a small number of Jews escaped because they agreed to be baptized “because of fear, rather than because of love of the Christian faith.” With all of the money taken from the Jews, Emico and “all that intolerable company of men and women then continued on their way to Jerusalem.”

This account highlights several elements analogous to the actions of modern terrorist groups. These include attempts at forced conversion; the murders of women and children; and the imposition of financial penalties on coerced converts who try to remain in their homes. Albert’s disparaging remarks about Emico also reveal that there were Christians who felt about the crusaders exactly the way many Muslims today surely feel if they are unlucky enough to find themselves in the path of violent lunatics.

In Mosul, the Iraqi city conquered by the Islamic State last June, Christians had coexisted for centuries with Muslims who did not share whatever medieval beliefs the terrorists claim to represent. The city was also home to the Yazidis, whose theology includes elements of Zoroastrianism as well as Islam and Christianity.

When the brutal warriors established control, thousands of Yazidis were forced to flee for their lives if they did not convert to Islam. Christians were also ordered to formally convert, pay taxes to Shariah courts or face “death by the sword,” without any possibility of escape.

Sound familiar?

Thomas Asbridge, director of the Center for the Study of Islam and the West at the University of London, commented in this newspaper that “we have to be very careful about judging behavior in medieval times by current standards.”

This issue is better judged from the other side of the looking glass. What we actually see today is a standard of medieval behavior upheld by modern fanatics who, like the crusaders, seek both religious and political power through violent means. They offer a ghastly and ghostly reminder of what the Western world might look like had there never been religious reformations, the Enlightenment and, above all, the separation of church and state.