In this Talk, I will talk about the results obtained for a sample of massive (above 10^10 Msun) galaxies at 1 < z < 1.5 for which we derived robust estimations of the star formation histories (SFHs). These galaxies benefit from the spectrophotometric resolution of the Survey for High-z Absorption Red and Dead Sources survey (SHARDS) in the GOODS-N field, together with grism observations from the CANDELS survey. Thanks to the unprecedented accuracy of the photometric redshift obtained using SHARDS and grism data, we were able to investigate the interplay between the environment, star formation histories, and level of star formation activity of these galaxies. I will also show the results obtained from the MAGAZ3NE survey, in the study of the largest spectroscopically confirmed sample of ultra-massive (above 10^11 Msun) galaxies at 3 < z < 4.