By universal agreement almost completely irrelevant militarily, an O was simply a beautiful place for lots of people to live, as well as being an elegantly devised and artistically detailed cultural achievement; why would anybody attack one? Developing civilisations and barbarian under-achievers aside, things had been acutely civilised and agreeably quiet in the greater galaxy for centiaeons; a working consensus regarding acceptable behaviour between the Involved had long since been arrived at, inter-cultural conflict resolution was a mature technology, pan-species morality had quite entirely moved on from the unfortunate lapses of days gone by and outright destruction of major civilisational assets was rightly seen by all as inelegant, wasteful, counter-productive and – apart from anything else – simply shrieking of shamefully deep societal insecurity.
This entirely civilised and not unreasonable assumption proved ill-founded when the Idirans – thinking to make it very clear to all concerned who were the fanatical, invincible ultra-warriors in the matter and who represented the hopelessly decadent, simpering, irredeemably civilian bunch of martial no-hopers merely playing at war – attempted to traumatise the Culture straight back out of their newly begun war by attacking and attempting to destroy every Orbital its war-fleets could reach.
An Orbital was just a fabulously thin bracelet of matter three million kilometres in circumference orbiting a sun, the apparent gravity on its interior surface provided by the same spin that gave it its day–night cycle; break one anywhere around its ten million kilometres circumference – and some were only a few thousand kilometres across – and it tore itself apart, unwinding like a released spring, dumping landscape, atmosphere and inhabitants unceremoniously into space.
All this came as something of a surprise. Natural disasters occurring to an Orbital were almost unheard of, the systems they inhabited having generally been cleared of wandering debris to form the material from which the O itself had been constructed, and even the most carefree, socially relaxed Orbitals packed a healthy variety of defensive systems easily able to pick off any remaining rocks and ice lumps that might have the temerity to approach.
However, against the sort of weaponry the Idirans – amongst many others – possessed, Orbitals were both effectively defenceless and hopelessly vulnerable. When the Idiran ships fell upon the Orbitals, the Culture was still mostly reminding itself how to build warships; the few war craft and militarised Contact ships it was able to put in the way of the attacks were swept aside.
Tens upon tens of billions died. And all for nothing, even from the Idiran point of view; the Culture, insufficiently traumatised perhaps, conspicuously failed to retreat from the war. Orders obeyed, damage duly inflicted, the Idiran war-fleets fell back to more martially relevant, not to say honourable, duties. Meanwhile the Culture – arguably to its own amazement as much as anybody else’s – had hunkered down, gritted what needed to be gritted, did the same regarding girding and, to the chorus of umpteen trillion people telling each other stoically, “It’s going to be a long war,” got grimly on with putting itself onto a proper war footing.
In the immediate aftermath of the attacks, many Orbitals, generally those closest to the action, were simply evacuated. Some were militarised, to the extent this made sense given they were so enormous and – patently, as had just been proved – fragile in the face of modern weaponry. Many were just left to revolve, empty, effectively mothballed. Some were destroyed by the Culture itself.
Orbitals could be moved, and some were, but it was an excruciatingly long-winded business. There was even, for this whole shifting-out-of-danger procedure, what was effectively a thing called a “waiting list”; a term and concept many devoutly pampered Culture citizens had some trouble getting entirely to grips with.
Regardless; having lots of pleasantly fitted-out buildings which could double as luxury lifeboats suddenly made unimpeachable sense. Even Orbitals almost certainly unreachably far away from the conflict took up the new construction trend, and giant skyscrapers, usually reassuringly sleek and ship-like in form, blossomed like colossal suddenly fashionable plants across the Culture’s Orbitals.
Distributed Cities came about when it was realised that even having the buildings/ships physically close to each other on the surface of an O was unwise, should an attack take place. Keeping them far apart from each other made the enemy’s targeting similarly distributed and confused. Fast, dedicated traveltube lines, in hard vacuum under the O’s outer surface, connected the buildings of any city cluster preferentially and directly, making the average journey time between buildings of any given city as quick or quicker than walking a conventional city block.