Here's a treat for connoisseurs of historical recurrence. The most powerful nation on Earth is going through a rough patch, fiercely unpopular abroad. Its armies are having trouble suppressing an insurgency on the banks of the Tigris, and the ruling oligarchy – in hock to vested interests and oil fortunes – doesn't know what to do about it. But this is AD117, not 2008, and the oil is extra virgin not black crude. Trajan is seriously ill and the empire is in crisis. Fortunately, a new incumbency is on the horizon, headed by a man who plans to pull the legions out of Mesopotamia. And, as it happens, he's the scion of an oil family, too: Publius Aelius Hadrianus, Trajan's named successor and, according to Dan Snow, in Hadrian, "one of the greatest Roman emperors of all time". The parallels between then and now will only go so far, of course. Hadrian's withdrawal from Mesopotamia caused some mutterings in Rome, so he quelled domestic uncertainty by declaring an amnesty on 900 million sesterces in back tax as well as doling out six gold coins to every citizen, a fiscal programme that I don't suppose will be available to the next president of the United States.
Hadrian is the subject of the British Museum's next big blockbuster exhibition, which provided sufficient justification for Dan Snow to pull out his Indiana Jones hat and hit the road in a 4x4, going to all four corners of the Roman world to look for evidence of how Hadrian stopped the rot. Walls appeared to be the principal answer, and not just the one that every English schoolboy knows about, but also a fortified wall that ran along most of the Roman Empire's eastern border in Europe, as well as quite astounding lengths of masonry out in the deserts of Africa, short stretches of which still stand. He wasn't averse to bolstering his rule with more complicated forms of architecture either, rebuilding an entire city at Cyrene in modern-day Libya, after the original had been torched by rebellious locals, and establishing Roman new towns wherever he thought that a bit of civic pomp might pin down the curling extremities of the empire.
Snow delivered his presentation at breathless pace, but then he can't have had a lot of time left over from the travelling, given an itinerary that stretched from the Roman granite mines in Africa to sites in Turkey and Jerusalem. Hadrian, incidentally, might have been big on infrastructure projects, but he wasn't much interested in multicultural outreach. He provoked a rebellion in Judaea by outlawing circumcision and planning to build a new capital on the Temple Mount. So great were the quantities of blood shed when he finally put down the resulting insurrection that farmers didn't need to use fertiliser for seven years, though one had the feeling that this fact hadn't actually been verified by independent experts. Despite his administrative and imperial success, things started going downhill for Hadrian after his lover, Antinous, drowned in the Nile and the end of his life was marked by ill health and paranoia. Having built what may have been the biggest retirement home in history, a villa complex two-thirds the size of Rome, he died without ever getting time to enjoy it.
Not a lot of Hadrian's building projects are still intact, apart from the Pantheon, which was taken over by the Christian church. Last night's The Seven Wonders of the Muslim World, a wrap-up of the programmes Channel 4 has been running all week, confirmed a crude rule of thumb: that reverence and a sense of beauty are better preservatives than fear or the profit motive. The Roman amphitheatre at Sagalassos is a ruin now, as are many of Hadrian's civic buildings, but the mosques and palaces visited in this series are still intact, even the one that is made out of mud. All of them will come to ruins in time, of course, but for now they exude an air of untouchable permanence.
The Seven Wonders of the Muslim World was driven by proselytising energy, hoping to convert its viewers not so much to Islam itself but to the intermediate notion that Islam isn't all about killing Westerners. It used the experiences of seven devout, Benetton-variegated Muslims to explore the essential tenets of the faith and seven of its most beautiful buildings. And very beautiful they were, too, contemplative spaces dignified, even for a non-believer, by what Larkin called a "hunger... to be more serious". I couldn't help wishing, though, that it was possible to have the buildings and the contemplation without the credulity and divisive certainties that accompany them. The image that really stuck in my mind – and in the director's too, apparently, since it was included more than once – was the road sign outside Mecca identifying separate lanes for Muslims and non-Muslims. Mosaics and hallowed spaces might be one side of religion, but that kind of grotesque absurdity is the other.