Topo-biography is not yet ‘a thing’, as far as I know, but perhaps it ought to be. A trip to Corsica twenty years ago left me, I felt, with a stronger understanding of the mindset of Napoleon. Because Corsica is hell. Not the people, you understand, but the landscape: an endlessly rocky terrain punctuated by impossible little hills, which the young Napoleon had to traverse on horseback as a military commander. With this kind of pedigree, surely it is little wonder that he went on to view the conquest of entire continents as an achievable objective.

Corsica was where Napoleon started life. Another island marked the end of it: St Helena, an East India Company possession in the South Atlantic, which, before the advent of steam power, functioned as a vital replenishment point for the India and China fleets. In 1815 the British government decided that this remote and defensible island might serve as a place of incarceration for one of Albion’s greatest enemies. Napoleon resided there for five and a half years, until his death in 1821. So what does St Helena say about the man?

Quite a lot, it turns out. Garden history tends to be condescended to as eternally peripheral, but it transpires that gardening was central to Napoleon’s experience of exile. The emperor – or ‘general’, as the British insisted on calling him – turned his mind to gardening when he arrived