Building walls ....

Trump is clearly not the first autocratic man to want to build a wall to protect his sand pit. China's Emperor Qin had a good crack at it. Berlin and Belfast's walls were not so visible from space but created their fair share of suffering. And in Britain ... Hadrian built 73 miles of symbolic power to delimit Empire from Barbarian (and judging by current politics I'm sure there's a few Scots who wished the wall was now a bit higher). With Hadrian's Wall came all the ingenuity that the Roman military industrial complex had to offer, including early renditions of blast barriers embedded in fort entrances to stop low wheeled enemy chariots rushing the gates.

Populating the forts along the course of the wall were some of the 56,000 soldiers in England at a time when the population as a whole was only four to five million. Troops came from Spain, Syria, Germany, North Africa with some attempting to serve out the 25 years it took to get Roman citizenship. Some stayed in the North, marrying into local communities and messing with the BNPs claim for some ancient, pure Britishness.

But not only did the Romans mix up the gene pool. According to our guide Colin, at Chester's Museum, Northumbria, they also bequested bits of the English language: 'fort' night (the amount of time you spent in the fort before returning to the main Roman camp); decimation (where every tenth man in a cohort was executed by his fellow soldiers when the cohort had done something naughty, like mutiny); 'you scratch my back' (after the need to get someone to scrape down your back to clean it in the communal baths); 'wrong end of the stick' (from the sticks with sponges on them used in the loo, and with the spongy bit obviously the wrong end you didn't want to get hold of).

The locals living around the excavated remnants have made an art of naming things after the wall: Hadrian's Haulage; Ale Ceasar; Hadrian Hotel etc. If Trump ever does get his border wall in the ground, I shudder to think that one day in the future, after it has crumbled like all walls and all empires governed by narcissists that think they will live forever, it will be excavated and put on show for tourists with a little gift shop nearby selling Trump lager, Trump chutney, and Trump fudge. As his wall is broken up and used in someone else's fence or road or sand pit, he will be reduced to a benign face on a tea towel.

Perhaps then, in the case of Trump's America, it is better to think of his wall as necessary for keeping his Barbarians in so they do as little damage as possible to the rest of the world.