Augustus, first emperor of Rome, invented a new genealogy, myth of origins, and history for himself and for Rome as he negotiated for authority with the Roman senate. As part of these negotiations the senate dedicated the Ara Pacis Augustae on the Campus Martius in 9 B.C.E. The function, location, and iconography of the monument participated in Augustus's attempts to link his present with the prehistory of Rome. In order for power and authority to be negotiated and legitimized, and for a history and myth to be invented, audience participation is required. This essay argues that the Ara Pacis Augustae was a symbol of the senate's participation and acceptance of Augustus's status, as well as a statement of its own power vis-à-vis that of the emperor.