The Weekend's Television: After Rome: Holy War and Conquest, Sat BBC2 The Devil's Whore, Sat, Channel 4 Louis Theroux: Law and Disorder in Johannesburg, Sun, BBC2

The jolly japes crusader

It wasn't an ideal weekend if you were hoping to spend less time with Boris Johnson. On Sunday, he turned up in the Reasonably Priced Car on Top Gear, hoping to expunge the memory of a particularly dismal track performance in an earlier visit, but finding traction something of a challenge on a day of heavy rain.

He's more at ease in the dry, really, when what's being tested is the speed with which he can power his way through 250 words of historical narrative, and there was plenty of scope for that on Saturday, in the second half of After Rome: Holy War and Conquest, his two-part series on the troubled relationship between Christianity and Islam.

He got off to a tyre-smoking start in Jerusalem, recalling the sack of the city by Christian knights in 1099, when the victors waded ankle-deep in blood and the bodies of the city's inhabitants were piled in pyramids "innumerable to all except God himself" – evidence, for any that still need it, that no religion has a monopoly on God-perfumed atrocity. In Johnson's words, the Crusader army was composed of "cranks... fizzing with religious fervour". But they were murderers, too, and ethnic cleansers and, but for a lack of means, genocidal maniacs as well, persuaded by Pope Urban the Second's lethal ecclesiastical propaganda that the Muslims they encountered were less than human.

That was the crux of the programme, really, if the term is not tactless in this context, that the actions of these zealous soldiers of Christ left an indelible impression behind them. In the most telling scene, Johnson sat on a sofa with several Muslim women and explained that the word "crusade" had now become so depleted of confessional animus in the West that it could be applied to litter campaigns or anti-binge-drinking programmes. Their astonishment made two things clear: that the word still carries something of the intensity that the word "holocaust" has here, and that George Bush could scarcely have chosen worse when characterising the war on terror.

Against the barbarities of Christian armies, Johnson set – without illusions – the comparative chivalry of Saladin and the intellectual achievements of Islamic Andalusia, which finally ended with the expulsion of the Moors, still a source of grievance to al-Qa'ida's equivalents of Urban the Second, now calling for their own Crusade. And he ended with an injunction to the audience to recall the oases rather than the desert when looking back on the story of the West and Islam, those moments when two civilisations intermingled and enriched each other rather than clashed in blood. "If we don't have the wit to escape from history, then let's at least try and relive the good bits," he concluded.

"The good bits" meant something very different in The Devil's Whore, episode three of which opened with a double execution, cutting between Angelica's hanging and the king's beheading. Eager bystanders pressing forward to dabble their handkerchiefs in Charles's blood counted as a good bit, or the execution of Leveller leaders at Burford churchyard, or a Cromwellian atrocity in an Irish church. Unfortunately, these historical good bits came so thick and fast that Angelica's interleaved drama was compressed to the point of absurdity. At one moment, she was being rescued from the gallows, next she was throwing her lot in with the Levellers, and then they'd chucked her out and she was on to the Ranters. It moved at such speed through some of the most fascinating episodes in English history that you felt almost as if you were watching a trailer for a drama rather than the thing itself, and there was very little time for Andrea Riseborough to establish much about her character other than her earnest devotion to feminism and her heavy-lidded allure, which had men of all camps offering a curiously doggy form of devotion. When I first wrote about the series, I suggested that it would involve a civil war between serious political drama and something more Gone with the Wind, in which the history provided a backdrop for more conventional melodrama. Sadly, given the time constraints, both sides appear to be losing.

In Louis Theroux: Law and Disorder in Johannesburg, our man spent time in the poorer districts of Johannesburg, places that make inner-city Philadelphia look like the choicer parts of Kensington. This time, Theroux wasn't riding alongside the police but the private-security companies that have sprung up to plug the gaping holes in South Africa's civil society. They plug it with unapologetic violence, or what one man called "medicine", a euphemism for serious beatings with a sjambok. Unnervingly, though, thieves may well prefer this rough justice to that of the local citizens, most of whom appear to believe that a death sentence is an appropriate punishment for minor robbery. The fact that one of the more successful security firms is called Bad Boyz probably tells you all you need to know about their approach to law enforcement. The film is well worth catching on iPlayer.