Twenty-one centuries ago, in the final decades of the Roman Republic, there was a standard path laid out for the ambitious young Roman politician. The “cursus honorum” – literally “course of honour”, though “ladder of office” gives more of a sense – was a list of jobs you had to hold in a specific order, if you wanted to make it to the top gig of consul.

There was also, in theory, a minimum age at which you could hold each post: 30 to be questor, 36 to be aedile and so forth. To prove you were a real high flier, it wasn’t enough to get the jobs, you had to reach them in the first year that you were eligible to do so.

And so, the biggest driving force of politics in the late Republic was neither serving the public nor changing the world: it was simply the urge to haul yourself up onto the next rung of the ladder as fast as you possibly could. This is probably a coincidence, but: the last years of the Roman Republic didn’t go terribly well.

There were other ways of attaining and projecting political power, of course, which as Republic turned to Empire became increasingly popular. Military conquest, and the triumphal processions that followed it. Grand monuments and architecture, into which you could literally carve your name. But again, the purpose of these achievements was not so much the glory of the state as that of the man who achieved them. Their primary function was to guarantee his place in the history books.

I'm uncomfortably aware that starting a column about Boris Johnson with a load of half-remembered guff about Roman history is quite a Boris Johnson thing to do, for which I can only apologise. But I stand by it, because I can't help but wonder whether, classicist that he is, it tells us something about how he understands politics.

What, after all, does Johnson want? We all know – as we have known, whether we wanted to or not, for what feels like several centuries now – that he desperately wants to be prime minister. Yet why he wants that job is quite difficult to discern. Thatcher wanted to remake the British economy; Blair to remake the Labour Party. Even David Cameron seems to have had some sense of purpose, in shrinking the state and (this part is quite funny now) providing stability. So what does Boris Johnson think a Johnson premiership is for?

Over the last few months, of course, the former foreign secretary has sold himself primarily as the only man who can actually bring Britain out of the EU. But we all know that's mostly there to win over the Tory selectorate; and the story about him writing two columns, one pro-Leave and one pro-Remain, before the referendum is a reminder that he could and did imagine himself going in the exact opposite direction on this one.

What else does he want? Tax cuts for the rich? Well probably, but he's a Tory, that's pretty much the job description. To support business? Only when it's convenient.

His eight years as mayor of London provide few clues to anything but his ambition. He had little interest in social policy or addressing the housing crisis, and seemed unenthusiastic about the long-term efforts required to do anything much in transport. The few things he seemed genuinely excited about were those that he could make happen relatively quickly, and which left a mark on the physical world: those ghastly new buses which on a summer's day double as slow cookers; the Garden Bridge, which never happened; the cable car, which unfortunately did. His continued enthusiasm for building literal bridges suggests he retains this keenness for leaving a mark on the world; the unbridled stupidity of most of the schemes he supports suggest a lack of concern about how he does it.

In other words, everything Boris Johnson has said or done has had one of two goals: to create a monument to himself; or to move himself one step closer to the next big job. Like the ideologies of the Romans he spends so much time misquoting, Johnsonism is no more and no less than the idea that Boris Johnson should be remembered.

There's an irony here, which is about the only upside I can find in this leaking cesspit of a political situation. Boris Johnson has dedicated his entire career to getting his name in the history books. But the manner in which he's done it means he stands to inherit the premiership three months before Brexit Day, with no way forward that won't detonate either his government or the entire British economy. It's quite plausible that he’s now within a year of the end of his political life.

Everything Boris Johnson has done has seemingly had the single purpose of ensuring that he gets a place in the history books. And why not? The Black Death’s in there. We remember disasters, too, if they’re catastrophic enough.