  Data from the AGS experiment E866 on charged particles emitted in central
Au+Au collisions at 10.8 AGeV incident energy is reviewed. The study of
spectral shapes indicates the presence of collective transverse flow and - in
particular for charged pions - of Coulomb final state interaction between
emitted particles and the nuclear charge distribution. The comparison to SIS
pion data measured with KaoS elucidates the role of charged pions to probe
nuclear reaction dynamics at lower incident energies.
