  It is known that the event horizon of a black hole can often be identified
from the zeroes of some curvature invariants. The situation in lower dimensions
has not been thoroughly clarified. In this work we investigate both (2+1)- and
(1+1)-dimensional black hole horizons of static, stationary and dynamical black
holes, identified with the zeroes of scalar polynomial and Cartan curvature
invariants, with the purpose of discriminating the different roles played by
the Weyl and Riemann curvature tensors. The situations and applicability of the
methods are found to be quite different from that in 4-dimensional spacetime.
The suitable Cartan invariants employed for detecting the horizon can be
interpreted as a local extremum of the tidal force suggesting that the horizon
of a black hole is a genuine special hypersurface within the full manifold,
contrary to the usual claim that there is nothing special at the horizon, which
is said to be a consequence of the equivalence principle.
