This is essentially a SF novel, but it does not contain any blasters, laser guns or alien spaceships. What it does contain is Alexander the Great, Genghis Khan and their armies pitched against each other at the walls of Babylon.
Most of you are likely to know who Arthur C Clarke is, if you don't, well he is a SF writer and he is so bloody good that he was knighted for it. Some of you might also know Stephen Baxter he is also a rather good SF writer, now they have just written a new book, Time's Eye and it is based around a rather mind-engaging event, called Discontinuity
What happened is that by some alien intervention(btw Clarke's aliens are always on another level from little/big green/grey men) earth has been ruptured and sown back together not in space, but in time. Basically the geography stayed the same, Sahara was still in North Africa, but different bits of Sahara throughout time were torn out and sown together, so there appeared random patches of dense rainforest in the midst of it, some areas were torn out of the Ice Age, so glaciers appeared in London, but all of it was patchwork. The interesting bit comes with humans - Alexander's army was time-shifted while in India, and so was Genghis Khan's horde and so was a Little Bird helicopter from 2037 in Afghanistan and so was a British fort nearby, Babylon was time-shifted as well, but some parts were newer than others, etc. Basically the book terminated with Alexander and the British fighting Genghis and then trying to rebuild his empire from Babylon, using some of the technology offered by the 21st century chopper crew. And throughout all that there were unexplainable spheres hanging in the air, impossible to move or dent and their radius to circumference ratio was exactly 3, not pi.
The book is absolutely awesome and draws you in like a whirlpool, haven't read anything of that scope for ages.