  Cosmological simulations predict the Universe contains a network of
intergalactic gas filaments, within which galaxies form and evolve. However,
the faintness of any emission from these filaments has limited tests of this
prediction. We report the detection of rest-frame ultraviolet Lyman-alpha
radiation from multiple filaments extending more than one megaparsec between
galaxies within the SSA 22 proto-cluster at a redshift of 3.1. Intense star
formation and supermassive black-hole activity is occurring within the galaxies
embedded in these structures, which are the likely sources of the elevated
ionizing radiation powering the observed Lyman-alpha emission. Our observations
map the gas in filamentary structures of the type thought to fuel the growth of
galaxies and black holes in massive proto-clusters.
