[en] In Experiment E866 at the AGS, it is now possible to study collective phenomena in relativistic Au+Au reactions by examining correlations of single and multi-particle observables with the collision reaction plane measured on an event-by-event basis. The influence of spectator matter on these observables remains one of the key unknowns in the study of relativistic heavy ion collisions. In addition, collective phenomena, such as hydrodynamical flow, are now recognized as one of the few experimentally accessible observables which show differences between cascade codes and models which may explicitly incorporate an equation-of-state