Published online by Cambridge University Press: 19 March 2015
We study the Euler–Lagrange flow of a Tonelli Lagrangian on the 2-torus   $\mathbb{T}^{2}$  at a fixed energy level
 $\mathbb{T}^{2}$  at a fixed energy level   ${\mathcal{E}}\subset T\mathbb{T}^{2}$  strictly above Mañé’s strict critical value. We prove that, if for some rational direction
 ${\mathcal{E}}\subset T\mathbb{T}^{2}$  strictly above Mañé’s strict critical value. We prove that, if for some rational direction   ${\it\zeta}\in S^{1}$  there is no invariant graph
 ${\it\zeta}\in S^{1}$  there is no invariant graph   ${\mathcal{T}}\subset {\mathcal{E}}$  over
 ${\mathcal{T}}\subset {\mathcal{E}}$  over   $\mathbb{T}^{2}$  for the Euler–Lagrange flow with the property that all orbits on
 $\mathbb{T}^{2}$  for the Euler–Lagrange flow with the property that all orbits on   ${\mathcal{T}}$  have an asymptotic direction equal to
 ${\mathcal{T}}$  have an asymptotic direction equal to   ${\it\zeta}$ , then there are chaotic dynamics in
 ${\it\zeta}$ , then there are chaotic dynamics in   ${\mathcal{E}}$ . This implies that, if the topological entropy of the Euler–Lagrange flow in
 ${\mathcal{E}}$ . This implies that, if the topological entropy of the Euler–Lagrange flow in   ${\mathcal{E}}$  vanishes, then in
 ${\mathcal{E}}$  vanishes, then in   ${\mathcal{E}}$  there are invariant graphs for all asymptotic directions
 ${\mathcal{E}}$  there are invariant graphs for all asymptotic directions   ${\it\zeta}\in S^{1}$  and integrable-like behavior on a large scale.
 ${\it\zeta}\in S^{1}$  and integrable-like behavior on a large scale.