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.
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