The Rambam in MT Shabbat 14:1 defines a Reshut HaRabbim as including not only roads and market squares but also wildernesses and forests. Commentators clarify the inclusion of wildernesses and forests, to mean such places if traversed by multitudes such as caravan routes in the desert and paths in the forest. The Rambam agrees that if an area is walled off with actual walls that the enclosed area no matter how large will no longer be a Reshut HaRabbim.
The Rambam does not accept the need for a roadway being at least 17 amot or that there be 600,000 person traversing but only that the area be traversed by the public; and that only an enclosure made up of actual walls can remove remove the Reshut HaRabbim designation (although gates at the walls are only required by him to be able to be closed but not actually periodically closed).
Could there be an eruv in a major town or city accordance with the plain meaning of Rambam's pesak?
