When I open a book called The Fourth Crusade I sort of expect to read about the Fourth Crusade, so the preface to Jonathan Phillips’s The Fourth Crusade came as a speed bump. It’s a two-page argument that the “holy war” has no equivalent in modern Western societies—we’ve given it up for the “just war,” so good on us. It became easier to understand what the hell this was doing here when I checked the copyright. This book about a turn-of-the-thirteenth century European army whose targets had nothing to do with the stated purpose of their war would have been getting its final polish at about the time George W. Bush’s Iraq war was getting started. The preface is a troll prophylactic. “I’m not criticizing the Fearless Leader!” says Jonathan Phillips. “Honest!”

Once you’re past the prologue this is a readable layman’s overview of a war that, even by crusading standards, was pure sleaze from start to finish. It started with propaganda: a round of sermons exhorting the faithful to head out and take Jerusalem back from the Moslems. (Wikipedia gives most of the credit to Fulk of Neuilly. According to Phillips the guy didn’t actually do a hell of a lot, but I wanted to mention him because I like the name “Fulk.” More parents should name their kids Fulk, is what I say.) Some people signed on, partly out of self-interest: crusading would buy them forgiveness for their sins. Which was great, because by the time a crusade was over they’d need it.

The guys who arranged for Venice to ship the crusaders to the holy land wildly overestimated the number of people willing to leave home for years at a time to fight Muslims on the other side of the world. (“We’ll have tens of thousands of crusaders! Seriously, dude!”) So the Venetians preempted all their trade for the year to make way for the army. Which, like so much in life, turned out to be less than was promised.

This was bad, because the army was covering the cost of shipping. The money the crusaders put up was supposed to be an investment; they would make it all back, with massive bonuses, in loot. So not much different from Wall Street, then. But this tiny army couldn’t cover the Venetians’ fees.

Not to worry—the Venetians had a solution. All the crusaders had to do was lean on this city, Zara, which hadn’t been showing proper respect to the legitimate businessmen of Venice. And then maybe head over to Byzantium, because a disposessed prince was offering a pretty good fee to take back the throne—and, yeah, the Byzantines were Christians rather than Moslems, but they weren’t the right kind of Christians, were they? And the crusaders could loot the place, so, hey, bonus!

Somehow the army never got around to taking Jerusalem.

You might conclude—and many historians do—that the crusaders, or at least their leaders, weren’t seriously devout and weren’t honest about the real purpose of their mission. Jonathan Phillips argues that their faith was just as sincere, and as motivating, as their lust for profit or their aspirations to perform valorous deeds. These guys did think they were doing God’s work, even as they hid the Pope’s threats of excommunication from their soldiers. It’s not that they never noticed the gap between their rhetoric and their actions. They convinced themselves to ignore it. As bad as the siege of Zara was, it would theoretically take them one step closer to the Holy Land. God can’t complain about that, can he?

It’s a common notion that people get their values from their religion. I’m not convinced that’s true in all, or even most, cases. I think most people start with certain values, and interpret their religion to match.

Most religious texts are long and complex. They’re poetry, not engineering manuals. Many are the work of multiple authors, transmitted through multiple, falliable scribes, and naturally contradictory. All of this is true of the Bible, and it would be easy for any crusading 12th century preacher to interpret the scriptures as he pleased. Modern readers still interpret the Bible in a hundred different ways. Liberal Christians take Jesus’s call to help the poor and downtrodden to heart; conservative Christians focus on the parts that condemn homosexuals. Take things far enough, and some groups will even rewrite holy writ to suit their ideology. In some ways the human race hasn’t come far since 1204.