  We present the results of the kinematic study of the extended gas in a sample
of 10 high redshift radio galaxies (z~2.5) based on high signal to noise Keck
II and VLT long slit spectroscopy. In addition to the typical high surface
brightness kinematically perturbed regions (FWHM and velocity shifts >1000
km/s), we find in all objects giant low surface brightness halos which show
quieter kinematics with typical emission line FWHM and velocity shifts of
\~several hundred km/s. The giant halos often extend for more than 100 kpc and
sometimes beyond the radio structures. Their emission line specta are typical
of high redshift active galaxies. Continuum is also often detected. The halos
are enriched with heavy elements at tens of kpc from the active nucleus. The
quasar continuum is the dominant source of ionization of the quiescent halos
along the radio axis. The detection of giant quiescent halos in all objects
suggests that they could be a common ingredient of high redshift radio
galaxies. The radio galaxies seem to be embedded within the halos. The nature,
origin of the halos and the cosmological implications are also discussed.
