Physics of heavy-ion collisions at SIS

A brief account of the presently ongoing studies of compressed hadronic matter formed in relativistic nucleus-nucleus interactions has been given. The observed radial expansion of the collision zone with average collective particle velocities of ∼ 0.3 . c is consistent with the formation of compressed hadronic matter at baryon densities of 2-3 times normal nuclear matter density. The hadro-chemical composition of the compressed matter, i.e. the fraction of excited baryon resonances has been analyzed by systematic studies of meson production. (author)