Strong correlation between the median Einstein radii θ_E,med and the strong-lensing cross sections σ_7.5 of a sample of massive clusters with masses M > 5 × 10¹⁴  M_⊙   h^-1 and redshifts z_l > 0.5 extracted from the MareNostrum Universe. The red solid line indicates the best linear fit relation between log (σ_7.5) and log (θ_E,med) (figure from Meneghetti et al. 2011).