I don't know since I haven't read it. It could be the founders of the city, or people who played significant roles in its early development, like a visionary leader or a great builder.
There's no way to be certain without reading the novel. However, it's possible that the main characters include an old storyteller who passes down the tales of the city's origin, a young adventurer who discovers secrets about the city's past, or a family that has been in the city since its very beginning and has witnessed all the changes and growth.
Since we don't have details about this 'city primeval novel', the main characters might be those who faced challenges in the primeval city. It could be a detective - like figure if the story has elements of crime and mystery in the early city, or it could be a group of settlers trying to make a new life for themselves.