We present Bema, a multimodal user interface that enables scholars of Greek rhetoric and oratory to perform virtual reality studies of ancient political assemblies at the hill of the Pnyx. Named after the flat stone speakers' platform utilized at the Pnyx, the Bema interface supports the high-level task of gaining a nuanced understanding of what it would feel like to give or receive a speech together with as many as 14,000 Athenian citizens and, further, how this experience must have changed as a result of at least two massive renovations captured in the archaeological record. Bema integrates solutions for several low-level interaction tasks, including navigating in virtual space and time, adjusting data visualization parameters, interacting with virtual characters, and analyzing spatial audio and architecture. Navigation is accomplished through a World-in-Miniature technique, re-conceived to support multi-touch input within a 4-wall Cave environment. Six degree-of-freedom head tracking and a sound level meter are used to analyze speeches delivered by users. Comparative analysis of different historical phases and assembly sizes is facilitated by the use of crowd simulation to generate realistic spatial arrangements for the assemblymen and staged animated transitions that preserve context while comparing two or more scenarios. An evaluation with our team's scholar of ancient Greek rhetoric and oratory provides support for the most important design decisions and affirms the value of this user interface for experiential analysis.