  The analysis of anisotropic flow of particles created in high energy
heavy-ion collisions gives insight into the early stage of these reactions.
Measurements of directed flow (v1), elliptic flow (v2) and flow of 4th and 6th
order (v4 and v6) are presented. While the study of v2 for multi-strange
particles establishes partonic collectivity the results for higher order
anisotropies constrain the initial conditions of hydrodynamic model
calculations.
