  A model for the evolution of ultrarelativistic heavy-ion collisions at both
CERN SPS and RHIC top energies is presented. Based on the assumption of
thermalization and a parametrization of the space-time expansion of the
produced matter, this model is able to describe a large set of observables
including hadronic momentum spectra, correlations and abundancies, the emission
of real photons, dilepton radiation and the suppression pattern of charmonia.
Each of these obervables provides unique capabilities to study the reaction
dynamics and taken together they form a strong and consistent picture of the
evolving system. Based on the emission of hard photons measured at SPS, we
argue that a strongly interacting, hot and dense system with temperatures above
250 MeV has to be created early in the reaction. Such a system is bound to be
different from hadronic matter and likely to be a quark-gluon plasma, and we
find that this assumption is in line with the subsequent evolution of the
system that is reflected in other observables.
