Starting from the notion of BN-pair (which is closely related to the concept of Tits building), we explain, following a classical insight, how one interprets buildings and their automorphism groups over the nonexisting ``field with one element". (As such, the symmetric groups become Chevalley groups over this ``field".) We then introduce scheme theories in ``characteristic one", and show how these are governed by a deep combinatorial (and motivic) nature.