  We present the discovery and detailed observations of the radio galaxy
1243+036 (=4C 03.24) at a redshift of $z=3.57$.
  The most spectacular feature of 1243+036 is the presence of a Ly$\alpha$ halo
of luminosity $\sim10^{44.5}$ ergs s$^{-1}$ which extends over$\sim20''$ (135
kpc). The narrow band imaging and the high resolution spectroscopy show that
the Ly$\alpha$ gas has three distinct components: (i) gas with a high velocity
dispersion (1550 km s$^{-1}$ FWHM) located inside the radio structure, (ii)
enhanced Ly$\alpha$ emission blue shifted by 1100 km s$^{-1}$ at the location
of the strong bend in the radio jet and (iii) Ly$\alpha$ emission extending out
well beyond the radio lobes. This emission has a low velocity dispersion (250
km s$^{-1}$ FWHM) and a velocity gradient of 450 km s$^{-1}$ over the extent of
the emission, indicative of large scale rotation.
  On the basis of these obserserations various mechanisms for the origin and
kinematics of the Ly$\alpha$ halo are discussed.
