  The results of a deep spectroscopic campaign on powerful radio galaxies with
redshifts z ~ 1, to investigate in detail their emission line gas properties,
are presented. Both the 2-dimensional velocity structure of the [OII] 3727
emission line and the ionisation state of the gas are found to be strongly
dependent upon the linear size (age) of the radio source in a manner indicative
of the emission line properties of small (young) radio sources being dominated
by the passage of the radio source shocks. The consequences of this evolution
throughout the few times 10-to-the-7 year lifetime of the radio source are
discussed, particularly with relation to the alignment of the UV--optical
continuum emission of these objects along their radio axis, the nature of which
shows similar evolution.
