Looking at random parts of the sky with Hubble, astronomers have found what appears to be the most distant protocluster ever seen: five galaxies in the process of growth, forming a cosmic collection that may grow into a massive cluster. The project, called the Brightest of Reionizing Galaxies (BoRG! ha!) survey, examined many images from Hubble. The galaxies are incredibly faint to the eye -- you'd have a hard time seeing them in the image without their locations marked -- but are intrinsically incredibly bright. They're located at a distance of something like 13.1 billion light years away! That means they were forming shortly after the Universe itself did, 13.7 billion years ago!
It's not yet confirmed if the five galaxies are bound together by gravity; the method used to get their distances isn't accurate enough. They'll need to follow up with spectroscopic observations to find that out. If they are connected gravitationally, then they will eventually form the core of a massive cluster of galaxies like the nearby Virgo Cluster, which boasts 2000 members. But as we see them back then, when the Universe itself was so young, they are still just in the process of initial growth (each is smaller than the Milky Way).
And how do they grow? By assimilating material around them. This is how the BORG cluster grows.