  Galaxy clusters are the most massive systems in the known universe. They host
relativistic cosmic ray populations and are thought to be gravitationally bound
by large amounts of Dark Matter, which under the right conditions could yield
to a detectable $\gamma$-ray flux. Prior to the launch of the Fermi satellite,
predictions were optimistic that Galaxy clusters would be established as
$\gamma$-ray bright objects by observations through its prime instrument, the
Large Area Telescope (LAT). Yet, despite numerous efforts, even a single
cluster detection is still pending.
