  We present extensive UBVR photometry of the Galactic globular cluster (GGC)
NGC6712 obtained with the ESO Very Large Telescope (VLT) which reach down to
two magnitudes below the main sequence turn-off and allows us for the first
time to determine the age of this cluster. By using the apparent luminosity of
the zero age horizontal branch (ZAHB), $V_{ZAHB}=16.32\pm0.05$ and the stellar
main sequence (MS) turn--off (TO) magnitude $V_{TO}=19.82\pm0.10$, we obtain
$\Delta V_{TO}^{HB}=3.5\pm0.1$ (a value fully compatible with that derived for
other clusters) which suggests that, at an age of $\sim 12$ Gyr, NGC 6712 is
coeval with other GGC of similar metallicity.
  We derive interstellar reddening by comparing the position and morphology of
the red giant branch (RGB) with a wide variety of reference clusters and find
$E(B-V)=0.33\pm0.05$, a value significantly lower than had been determined
previously. Assuming this value for the reddening, we determine a true distance
modulus of $(m-M)_0 = 14.55$, corresponding to a distance of $\sim 8$ kpc.
  We find a population of 108 candidate blue straggler stars (BSS),
surprisingly large when compared with the typical BSS content of other low
concentration clusters. Moreover, we detect a very bright blue star in the core
of NGC6712 that might be a post-AGB star. These results, combined with those
already presented in two companion papers, strongly support the hypothesis that
NGC6712 was, at some early epoch of its history, much more massive and
concentrated. The continued interaction with the bulge and the disk of the
Galaxy has driven it toward dissolution, and what we now observe is nothing but
the {\it remnant} core of a cluster that once was probably one of the most
massive in the Galaxy.
