While in QED the ladder approximation caused problems with crossing symmetry and gauge invariance, indicating the inclusion of crossed-ladder terms. In quantum chromodynamics (QCD) this approximation is frequently used phenomenologically to calculate hadron mass and its structure in terms of Bethe--Salpeter amplitudes and Faddeev amplitudes, a well-known Ansatz of which is proposed by Maris and Tandy. Such an Ansatz for the dressed quark-gluon vertex within the rainbow-ladder truncation respects chiral symmetry and its dynamical breaking, which therefore is an important modeling of the strong nuclear interaction. As an example the structure of pions can be solved applying the Maris--Tandy Ansatz from the Bethe--Salpeter equation in Euclidean space.