Let X be a n-dimensional (smooth) intersection of two quadrics, and let T*X
be its cotangent bundle. We show that the algebra of symmetric tensors on X is
a polynomial algebra in n variables. The corresponding map F: T*X -- > C^n is a
Lagrangian fibration, which admits an explicit geometric description; its
general fiber is a Zariski open subset of an abelian variety, quotient of a
hyperelliptic Jacobian by a 2-torsion subgroup. For n = 3 F is the Hitchin
fibration of the moduli space of rank 2 bundles with fixed determinant on a
curve of genus 2