Meanwhile, the sheer size of the Ringworld kept generating new stories. Ultimately Niven wrote two more sequels, The Ringworld Throne (1996) and Ringworld's Children (2004). Ringworld's Children was inspired directly by conversations with fans on the larryniven-l e-mail list. And future sequels haven't been ruled out, either. Of the Pak who built the structure, Niven writes: "They must have found some way to cooperate, just to cross 30-odd thousand light years of space at sublight speeds. The protectors who reached Ringworld space must have been significantly altered from classic Pak... but that's a tale I haven't told yet. I have notes."