The Chandra Deep Field South (CDFS) is one of the most extensively observed regions of the sky, with some of the deepest multi-wavelength coverage ever: Chandra and XMM-Newton X-ray observations, multi-band HST-ACS optical imaging and mid- to far-IR Spitzer observations included in the GOODS and SWIRE legacy programs, extensive deep ground-based imaging and spectroscopy with 8-m class telescopes such as the VLT and, finally, deep 1.4-GHz radio observations with the ATCA and the VLA. We are currently using the GMRT to image this field at 327 MHz to very deep levels, which is allowing us a first detailed glimpse of the nature of Ultra Steep Spectrum sources and optically unidentified radio sources at the very faintest radio flux levels.