@Eisenhardt2008; @Muzzin2009; @Galametz2012; @Wylezalek2013; @Rettura2014]. The criterion proposed by @Papovich2008 uses a 3.6$-$ 4.5colour selection to isolate all types of galaxies at $z>1.3$, thanks to the peak of stellar emission near 1.6in galaxy spectral energy distributions (SEDs) moving into these bands at $z>1$. This feature is present in galaxies of all types so selecting only on this criteria does not greatly bias the galaxy selection.

One very successful *Spitzer* survey is the Clusters Around Radio-Loud AGN survey [CARLA; @Wylezalek2013; @Wylezalek2014], which imaged over 400 fields surrounding RLAGN, and identified $\sim200$ cluster and protocluster candidates at $1.3<z<3.2$. Using the *Spitzer* wavebands to select both star forming and passively evolving cluster members, these clusters can be used to investigate whether RLAGN are biased tracers of clusters that reside preferentially in younger structures, or whether the young structures discovered to date are due to the protocluster confirmation techniques used.

Based on deep optical imaging, @Cooke2015 identified a subset of the densest CARLA fields that show signs of being mature clusters, exhibiting red sequences, and dense cores of red galaxies. Here we examine one of these fields, around the RLAGN C (Figure \[fig:fieldimg\]). @Lacy1999 tentatively assigned a redshift to this galaxy of $z=1.95$ based 