Some details become clues to the nature of the Builders.

The plethora of harbors and fjords, plus the shallow oceans (most of them), suggest a race that uses only the top of an ocean.

The nastier life forms — mosquitoes, flies, jackals, sharks, vampire bats — dont exist. Hominids have moved into some of those ecological slots. The Engineers werent ecologists, they were gardeners.

The inhabitants are hominids in bewildering variety, some intelligent, some not. They fill ecological niches which on Earth are held by almost any mammal, but particularly the nastier life forms, jackals and wolves and vampire bats… as if mankinds ancestor, Homo habilis, had been protected until they numbered hundreds of billions, then abandoned to mutate endlessly.

You dont know the Ringworld until youve grasped its size.

After the book came out, a friend was going to build a scale model for an upcoming convention. He had a marble, a blue immy, to serve as the Earth, for scale. Turns out hed need a ribbon five feet tall and half a mile long. The hotel wasnt big enough.

One guy who tried to map the Ringworld told me he ran out of computer space very rapidly. He ran into too many powers of ten.

David Gerrold speaks of a class of novel called "the Enormous Big Thing." Today you could fill a fair-sized shelf with them. Arthur C. Clarkes Rendezvous with Rama and Bob Shaws Orbitsville are in that class, and so is my own Rainbow Mars.

But Ringworld came first, published in 1970.

It might have been laughed at. Too big, too improbable. Any normal structural material would be torn apart by its spin. I waited for the reviews in some fear.