in greatly altered form

During the course of my own career I've made use of altered history again and again to provide the impetus for a story. In "Translation Error," back in 1959, I had an emissary from another world take steps to avert World War I so that the second World War, which would lead to the development of atomic weapons, would also not take place. My novel of 1967, The Gate of Worlds, proposed that the Black Death of 1348 had killed so many Europeans that the Ottoman Turks had been able to conquer the whole continent, leaving the New World to develop independently under Aztec and Inca ruler and Africa as a continent of black-ruled kingdoms. And in "Trips," a short story from 1975, I packed a dozen or more alternative worlds into a single
work less than thirty pages long, in which my protagonist drifts from one reality to another: in one section, Genghis Khan has created a worldwide Mongol empire, in another, President Roosevelt's retirement in 1940 has led to American neutrality and a German victory in World War II, and in another, John F. Kennedy was never assassinated. Finally my wanderer returns to what he takes to be the real world, his own world, our world, from which he had originally departed -- only to discover that he hasn't reached home after all, for this world, too, similar as it is to the one from which he first set out, is also an alternative reality, in which another version of himself is living in the house he takes to be his own. And in a story called "Needle in a Timestack" (1983) I devised a 21st-century society in which time machines are as ubiquitous as cell phones and people are constantly scrambling other people's lives by making changes in their pasts.

My most elaborate venture into alternative reality, though, is the novel Roma Eterna (2003), which portrays, in ten sections spanning fifteen hundred years, a world in which the Roman Empire never fell apart, and is still -- in greatly altered form -- ruling the world in the twentieth century. The best way I know to show you how such visions of alternative reality are created is to describe, step by step, the process by which I constructed that book. What was the key factor, I asked myself, in the collapse of Imperial Rome? Isolate that factor, remove it from history, and, at least for the purposes of my story, Rome would withstand all challenge and survive through the ages.

I had been reading, just then, The Decline and Fall of the Roman Empire, the classic work of the eighteenth-century historian Edward Gibbon. It was Gibbon's thesis that the rise of Christianity, adopted as the official state religion by the fourth-century Roman Emperor Constantine, set in motion the forces that caused the crumbling of Roman power. There were other factors as well, of course -- the encroachment of barbarian tribes on the Roman borders, for example, and Rome's catastrophic decision to enlist barbarian troops in its own armies -- but Gibbon saw Christianity as a poisonous creed, preoccupied with sterile theological debate and focused on hypothetical rewards in a future existence in a supernatural world at the expense of a practical concentration on the problems of life in the here and now, and he felt that its spread had dealt the Empire its death-blow. "I have described the triumph of barbarism and religion," he said toward the end of his immense book, a famous sentence succinctly encapsulating his analysis of the Empire's decay.