  As a consequence of Koebe's retrosection theorem, every closed Riemann
surface of genus $g \geq 2$ is uniformized by a Schottky group. Marden observed
that there are Schottky groups which are not classical ones, that is, they
cannot be defined by a suitable collection of circles. This opened the question
to if every closed Riemann surface can be uniformized by a classical Schottky
group. Recently, Hou has observed this question has an affirmative answer by
first noting that every closed Riemann surface can be uniformized by a Schottky
group with limit set of Hausdorff dimension $<1$ and then by proving that such
a Schottky group is necessarily a classical one. In this paper, we provide
another argument, based on the density of Belyi curves on the the moduli space
${\mathcal M}_{g}$ and the fact that the locus ${\mathcal M}_{g}^{cs} \subset
{\mathcal M}_{g}$ of those Riemann surfaces uniformized by classical Schottky
groups is a non-empty open set. We show that every Belyi curve can be
uniformized by a classical Schottky group, so ${\mathcal M}_{g}^{cs}={\mathcal
M}_{g}$.
