  We classify the set of quadrilaterals that can be inscribed in convex Jordan
curves, in the continuous as well as in the smooth case. This answers a
question of Makeev in the special case of convex curves. The difficulty of this
problem comes from the fact that standard topological arguments to prove the
existence of solutions do not apply here due to the lack of sufficient
symmetry. Instead, the proof makes use of an area argument of Karasev and Tao,
which we furthermore simplify and elaborate on. The continuous case requires an
additional analysis of the singular points, and a small miracle, which then
extends to show that the problems of inscribing isosceles trapezoids in smooth
curves and in piecewise $C^1$ curves are equivalent.
