  We present a catalogue of 348 galaxy clusters and groups with $0.2<z<1.2$
selected in the 2.78 $deg^2$ ALHAMBRA Survey. The high precision of our
photometric redshifts, close to $1\%$, and the wide spread of the seven
ALHAMBRA pointings ensure that this catalogue has better mass sensitivity and
is less affected by cosmic variance than comparable samples.
  The detection has been carried out with the Bayesian Cluster Finder (BCF),
whose performance has been checked in ALHAMBRA-like light-cone mock catalogues.
Great care has been taken to ensure that the observable properties of the mocks
photometry accurately correspond to those of real catalogues. From our
simulations, we expect to detect galaxy clusters and groups with both $70\%$
completeness and purity down to dark matter halo masses of
$M_h\sim3\times10^{13}\rm M_{\odot}$ for $z<0.85$. Cluster redshifts are
expected to be recovered with $\sim0.6\%$ precision for $z<1$. We also expect
to measure cluster masses with $\sigma_{M_h|M^*_{CL}}\sim0.25-0.35\, dex$
precision down to $\sim3\times10^{13}\rm M_{\odot}$, masses which are $50\%$
smaller than those reached by similar work.
  We have compared these detections with previous optical, spectroscopic and
X-rays work, finding an excellent agreement with the rates reported from the
simulations. We have also explored the overall properties of these detections
such as the presence of a colour-magnitude relation, the evolution of the
photometric blue fraction and the clustering of these sources in the different
ALHAMBRA fields. Despite the small numbers, we observe tentative evidence that,
for a fixed stellar mass, the environment is playing a crucial role at lower
redshifts (z$<$0.5).
