  High-energy collisions of heavy ions provide a means to study QCD in a regime
of high parton density, and may provide insight into its phase structure.
Results from the four experiments at RHIC (BRAHMS, PHENIX, PHOBOS and STAR) are
presented, and placed in context with the lower energy data from the AGS and
SPS accelerators. The focus is on the insights these measurements provide into
the time history of the collision process. Taken together, the data point to
the creation of a deconfined state of matter that forms quickly, expands
rapidly and freezes out suddenly.
