Richard J.A. Talbert 
The Senate of Imperial Rome [PDF ebook] 

Richard J. A. Talbert examines the composition, procedure, and functions of the Roman senate during the Principate (30 B.C.-A.D. 238). Although it is of central importance to the period, this great council has not previously received such scholarly treatment. Offering a fresh approach to major ancient authors (Pliny and Tacitus in particular), the book also draws on inscriptions and legal writers never before fully exploited for the study of the senate.