  The young (~2 Myr) cluster Chamaeleon I is one of the closest laboratories to
study the early stages of star cluster dynamics in a low-density environment.
We studied its structural and kinematical properties combining parameters from
the high-resolution spectroscopic survey Gaia-ESO with data from the
literature. Our main result is the evidence of a large discrepancy between the
velocity dispersion (sigma = 1.14 \pm 0.35 km s^{-1}) of the stellar population
and the dispersion of the pre-stellar cores (~0.3 km s^{-1}) derived from
submillimeter observations. The origin of this discrepancy, which has been
observed in other young star clusters is not clear. It may be due to either the
effect of the magnetic field on the protostars and the filaments, or to the
dynamical evolution of stars driven by two-body interactions. Furthermore, the
analysis of the kinematic properties of the stellar population put in evidence
a significant velocity shift (~1 km s^{-1}) between the two sub-clusters
located around the North and South main clouds. This result further supports a
scenario, where clusters form from the evolution of multiple substructures
rather than from a monolithic collapse.
  Using three independent spectroscopic indicators (the gravity indicator
$\gamma$, the equivalent width of the Li line, and the H_alpha 10\% width), we
performed a new membership selection. We found six new cluster members located
in the outer region of the cluster. Starting from the positions and masses of
the cluster members, we derived the level of substructure Q, the surface
density \Sigma and the level of mass segregation $\Lambda_{MSR}$ of the
cluster. The comparison between these structural properties and the results of
N-body simulations suggests that the cluster formed in a low density
environment, in virial equilibrium or supervirial, and highly substructured.
