  The nuclear equation of state (EoS) is investigated by flow phenomena in
relativistic heavy-ion collisions, both in transverse and radial direction, in
comparison to experimental data from 150 A MeV to 11 A GeV. To this aim the
collective dynamics of the nucleus-nucleus collision is described within a
transport model of the coupled channel RBUU type. There are two factors which
dominantly determine the baryon flow at these energies: the momentum dependence
of the scalar ($U_S$) and vector potentials ($U_\mu$) for baryons and the
resonance/string degrees of freedom for energetic hadron excitations. We fix
the explicit momentum dependence of the nucleon-meson couplings by the nucleon
optical potential up to 1 GeV and extrapolate to higher energy. When assuming
the optical potential to vanish identically for $E_{kin} \geq 3.5$ GeV we
simultaneously describe the sideward flow data of the PLASTIC BALL, FOPI, EoS
and E877 collaborations, the elliptic flow data of the E895 and E877
collaborations and approximately the rapidity and transverse mass distribution
of protons at AGS energies without employing any {\it explicit} assumption on a
phase transition in the EoS. However, the gradual change from hadronic to
string degrees of freedom with increasing bombarding energy can be viewed as a
transition from {\it hadronic} to {\it string} matter, i.e. a dissolution of
hadrons at high energy density.
