  The resonant substructure of the decay $D^{0} \rightarrow \pi^{+} \pi^{-}
\pi^{+} \pi^{-}$ is studied by performing a full five-dimensional amplitude
analysis. Preliminary results based on data collected by the CLEO-c detector
are presented. This is the largest dataset of $D^{0} \rightarrow \pi^{+}
\pi^{-} \pi^{+} \pi^{-}$ decays analysed in this way to-date. The two most
significant contributions are $D^{0} \rightarrow a_{1}(1260)^{+} \pi^{-}$ and
$D^{0} \rightarrow \rho(770)^{0}\rho(770)^{0}$. The line shape, mass and width
of the $a_{1}(1260)$ resonance are determined, and model-independent studies of
the line shapes of several resonant contributions are preformed.
