|I met a traveller from an antique land
Who said: Two vast and trunkless legs of stone
Stand in the desert... Near them, on the sand,
Half sunk, a shattered visage lies, whose frown,
And wrinkled lip, and sneer of cold command,
Tell that its sculptor well those passions read
Which yet survive, stamped on these lifeless things,
The hand that mocked them, and the heart that fed:
And on the pedestal these words appear:
"My name is Ozymandias, king of kings:
Look on my works, ye Mighty, and despair!"
Nothing beside remains. Round the decay
Of that colossal wreck, boundless and bare
The lone and level sands stretch far away.
[Percy Bysshe Shelley, 1792-1822]
Christopher's trilogy The Tripods can be seen as a sort of alternative sequel to Well's The War of the Worlds. What if the Martians had not succumbed to bacteria, and had succeeded in their conquest -- what then? Wells's aliens would simply have destroyed humanity, but Christopher's have a sort of gloomy curiosity about the diversity of human customs, which they allow to persist. They are also physiologically different, though each has tentacles. It is the Tripods themselves which are dead ringers for Wells's Martian machines, as the following excerpt from Wells shows:
And this Thing I saw! How can I describe it? A monstrous tripod, higher than many houses, striding over the young pine trees, and smashing them aside in its career; a walking engine of glittering metal, striding now across the heather; articulate ropes of steel dangling from it, and the clattering tumult of its passage mingling with the riot of the thunder. A flash, and it came out vividly, heeling over one way with two feet in the air, to vanish and reappear almost instantly as it seemed, with the next flash, a hundred yards nearer. Can you imagine a milking stool tilted and bowled violently along the ground? That was the impression those instant flashes gave. But instead of a milking stool imagine it a great body of machinery on a tripod stand.
Then suddenly the trees in the pine wood ahead of me were parted, as brittle reeds are parted by a man thrusting through them; they were snapped off and driven headlong, and a second huge tripod appeared, rushing, as it seemed, headlong towards me. And I was galloping hard to meet it! At the sight of the second monster my nerve went altogether. Not stopping to look again, I wrenched the horse's head hard round to the right and in another moment the dog cart had heeled over upon the horse; the shafts smashed noisily, and I was flung sideways and fell heavily into a shallow pool of water.
I crawled out almost immediately, and crouched, my feet still in the water, under a clump of furze. The horse lay motionless (his neck was broken, poor brute!) and by the lightning flashes I saw the black bulk of the overturned dog cart and the silhouette of the wheel still spinning slowly. In another moment the colossal mechanism went striding by me, and passed uphill towards Pyrford.
Seen nearer, the Thing was incredibly strange, for it was no mere insensate machine driving on its way. Machine it was, with a ringing metallic pace, and long, flexible, glittering tentacles (one of which gripped a young pine tree) swinging and rattling about its strange body. It picked its road as it went striding along, and the brazen hood that surmounted it moved to and fro with the inevitable suggestion of a head looking about. Behind the main body was a huge mass of white metal like a gigantic fisherman's basket, and puffs of green smoke squirted out from the joints of the limbs as the monster swept by me. And in an instant it was gone.
So much I saw then, all vaguely for the flickering of the lightning, in blinding highlights and dense black shadows.
As it passed it set up an exultant deafening howl that drowned the thunder--"Aloo! Aloo!"--and in another minute it was with its companion, half a mile away, stooping over something in the field.
The Martians do not seem to have the wheel, and have mechanisms of leverage instead. The machines thump the ground, they have a hunting wail, they are later described as "a hundred feet high", they walk on three legs with a turning head, they have swirling metal tentacles.
Christopher himself, slightly apologetically, says:
It was... only after I'd finished the first book of the trilogy, at that stage myself still unsure what the Tripods were, that I realised I had unconsciously stolen the concept from a better writer.
These are not the only aspects of the The War of the Worlds influencing Christopher. For one thing, it's a narrative (as is John Wyndham's The Day of the Triffids). The narrator forages for raw vegetables in a kitchen garden, he visits a ruined city overgrown by plant life, and so on. These are now the staples of apocalyptic sci-fi. Viewers of the television Tripods may well recognise this scene, set in a cellar:
In the darkness I could just see the thing--like an elephant's trunk more than anything else--waving towards me and touching and examining the wall, coals, wood and ceiling. It was like a black worm swaying its blind head to and fro.
I stress "television" because the BBC has clearly also read the book, and it also influences their design. Some of the BBC Tripods have a heat ray, for instance.
The Tripods trilogy was written between 1967 and 1970, and carries echoes of the time. In 1968, cathartic student revolutions broke out in University campuses across the Western world, triggered mostly by the protest movement against the Vietnam war: the students demanded, amongst other things, liberation from authoritarian teaching methods. The society of Capping can be seen as a parable for this. (That John Christopher was interested in this edge of anarchy can be seen from his novel Pendulum. It's a theme also occurring in other late-60s fantasy and science fiction, such as the television drama The Prisoner.)
The late 1960s were also a time of high cold-war tension, in which the United Nations was almost entirely ineffectual: something which colours the close of the trilogy. Finally, it seems worth mentioning the space race. In 1968-9, crews of three astronauts were being selected for the Apollo moon landings, from a fiercely competitive astronaut corps: it seems reasonable to think this may have suggested the repeated sequences in which Julius must select from his troops, especially at the start of The City of Gold and Lead.