High resolution VLBI observations of relativistic jets are essential to constrain fundamental parameters of current jet formation models. At a distance of 249 Mpc, Cygnus A is a unique target for such studies, being the only powerful FRII radiogalaxy for which a detailed sub-parsec scale imaging of the base of both jet and counter-jet can be obtained. Observing at millimeter wavelengths unveils those regions which appear self-absorbed or free-free absorbed at longer wavelengths and enables an extremely sharp view of the nuclear regions to be obtained. We performed 3 and 7 mm Global VLBI observations, achieving ultra-high resolution imaging on scales down to 45 microarcseconds. With a spatial resolution of only ~200 Schwarzschild radii we could study the transverse size and structure at the onset of the two-sided flow through a pixel-based analysis. The flow appears already broad and stratified at the base, suggesting that the emission is produced by a slow outer sheath launched from the accretion disk.