  Using spectroscopic observations taken for the VIMOS Ultra-Deep Survey (VUDS)
we report here on the discovery of PCl J1001+0220, a massive proto-cluster
located at $z_{spec}\sim4.57$ in the COSMOS field. The proto-cluster was
initially detected as a $\sim12\sigma$ overdensity of typical star-forming
galaxies in the blind spectroscopic survey of the early universe ($2<z<6$)
performed by VUDS. It was further mapped using a new technique developed that
statistically combines spectroscopic and photometric redshifts, the latter
derived from a recent compilation of deep multi-band imaging. Through various
methods, the descendant halo mass of PCl J1001+0220 is estimated to be
$\log(M_{h}/M_{\odot})_{z=0}\sim14.5-15$ with a large amount of mass apparently
already in place at $z\sim4.57$. Tentative evidence is found for a fractional
excess of older and more massive galaxies within the proto-cluster, an
observation which suggests the pervasive early onset of vigorous star
formation. No evidence is found for the differences in the star formation rates
of member and a matched sample of coeval field galaxies either through
rest-frame ultraviolet methods or through stacking extremely deep Very Large
Array 3 GHz imaging. Additionally, no evidence for pervasive strong active
galactic nuclei (AGN) activity is observed. Analysis of Hubble Space Telescope
images provides weak evidence for for an elevated incidence of galaxy-galaxy
interaction within the proto-cluster. The spectral properties of the two
samples are compared, with a definite suppression of Ly$\alpha$ seen in the
average member galaxy relative to the coeval field
($f_{esc,Ly\alpha}=1.8^{+0.3}_{-1.7}$% and $4.0^{+1.0}_{-0.8}$%, respectively).
This observation along with other lines of evidence leads us to infer the
possible presence of a large, cool diffuse medium within the proto-cluster
environment evocative of a nascent intracluster medium.
