  We present an XMM-Newton observation of the radio galaxy 4C 23.56 at z=2.48
which reveals extended X-ray emission coincident with the radio lobes spanning
\~0.5 Mpc. These are the largest X-ray-bright lobes known at z>2. Under the
assumption that these features result from inverse-Compton scattering of cosmic
microwave background photons by relativistic electrons in the radio source
lobes, the measured luminosity of L_0.5-8 keV=7.5x10^44 erg s^-1 implies a
minimum energy stored within the lobes of ~10^59 erg. We discuss the potential
of the large-scale radio/X-ray lobes to influence evolution of the host galaxy
and proto-cluster environment at high redshift.
