  We present a weak lensing detection of filamentary structures in the cosmic
web, combining data from the Kilo-Degree Survey, the Red Cluster Sequence
Lensing Survey and the Canada-France-Hawaii Telescope Lensing Survey. The line
connecting luminous red galaxies with a separation of $3 - 5\,
h^{-1}\text{Mpc}$ is chosen as a proxy for the location of filaments. We
measure the average weak lensing shear around $\sim$11,000 candidate filaments
selected in this way from the Sloan Digital Sky Survey. After nulling the shear
induced by the dark matter haloes around each galaxy, we report a $3.4\,\sigma$
detection of an anisotropic shear signal from the matter that connects them.
Adopting a filament density profile, motivated from $N$-body simulations, the
average density at the centre of these filamentary structures is found to be
$15 \pm 4$ times the critical density.
