  For each $m\ge 1$, Roulleau and Urz\'ua give an implicit construction of a
configuration of $4(3m^2-1)$ complex plane cubic curves. This construction was
crucial for their work on surfaces of general type. We make this construction
explicit by proving that the Roulleau-Urz\'ua configuration consists precisely
of the Halphen cubics of order $m$, and we determine specific equations of the
cubics for $m=1$ (which were known) and for $m=2$ (which are new).
