  The X-ray source IGR J16318-4848 was the first source discovered by INTEGRAL.
The high energy spectrum exhibits such a high column density that the source is
undetectable in X-rays below 2 keV. We used the NTT telescope of ESO to obtain
optical and near-infrared (NIR) observations. We confirm the already proposed
NIR counterpart and for the first time extended detection into optical. We
report here photometric measurements in the R, I, J, bands, upper flux limits
in the Bb and V bands, lower flux limits in the H and Ks bands. We also obtain
NIR spectroscopy, revealing a large number of emission lines, including
forbidden iron lines and P-Cygni profiles, and showing a strong similarity with
CI Cam, another strongly absorbed source. These data point to a high
luminosity, high temperature source, with an intrinsic optical-NIR absorption
greater than the interstellar absorption, but two orders of magnitude below the
X-ray absorption. We propose that the source is a High Mass X-ray binary (HMXB)
at a distance between 0.9 and 6.2 kpc, the optical/NIR counterpart corresponds
to the mass donor, which is an early-type star, maybe a sgB[e] star, surrounded
by a dense and absorbing circumstellar material. This would make the second
HMXB with a sgB[e] star as the mass donor after CI Cam. Such sources may
represent a different evolutionary state of X-ray binaries previously
undetected with the lower energy space telescopes ; if it is so, a new class of
strongly absorbed X-ray binaries is being unveiled by INTEGRAL.
