Context : Hierarchical galaxy formation models indicate that during their lifetime galaxy clusters undergo several mergers . An example of such a merging cluster is Abell~2256 . Here we report on the discovery of three diffuse radio sources in the periphery of Abell 2256 , using the Giant Metrewave Radio Telescope ( GMRT ) . Aims : The aim of the observations was to search for diffuse ultra-steep spectrum radio sources within the galaxy cluster Abell 2256 . Methods : We have carried out GMRT 325  MHz radio continuum observations of Abell 2256 . V , R and I band images of the cluster were taken with the 4.2m William Herschel Telescope ( WHT ) . Results : We have discovered three diffuse elongated radio sources located about 1 Mpc from the cluster center . Two are located to the west of the cluster center , and one to the southeast . The sources have a measured physical extent of 170 , 140 and 240 kpc , respectively . The two western sources are also visible in deep low-resolution 115 - 165  MHz Westerbork Synthesis Radio Telescope ( WSRT ) images , although they are blended into a single source . For the combined emission of the blended source we find an extreme spectral index ( \alpha ) of -2.05 \pm 0.14 between 140 and 351 MHz . The extremely steep spectral index suggests these two sources are most likely the result of adiabatic compression of fossil radio plasma due to merger shocks . For the source to the southeast , we find that { \alpha < -1.45 } between 1369 and 325 MHz . We did not find any clear optical counterparts to the radio sources in the WHT images . Conclusions : The discovery of the steep spectrum sources implies the existence of a population of faint diffuse radio sources in ( merging ) clusters with such steep spectra that they have gone unnoticed in higher frequency ( \gtrsim 1  GHz ) observations . Simply considering the timescales related to the AGN activity , synchrotron losses , and the presence of shocks , we find that most massive clusters should possess similar sources . An exciting possibility therefore is that such sources will determine the general appearance of clusters in low-frequency high resolution radio maps as will be produced by for example LOFAR or LWA .