  High redshift radio galaxies are amongst the most massive galaxies in the
early Universe and have properties expected from central galaxies in forming
clusters. We are carrying out an observational programme on the VLT to find and
study galaxy proto clusters around radio galaxies at redshifts 2 < z < 4.
First, we use narrow band imaging to select candidate galaxies which show
excess Lyman alpha emission at redshifts similar to the central radio galaxy.
Then, we use multi object spectroscopy to confirm the redshifts of these
candidates and measure the velocity dispersion of the cluster members. Our goal
is to observe a sample of about 10 targets and investigate galaxy overdensities
as a function of redshift. Here, we report on the current progress of the
programme and show some preliminary results which include the discovery of a
structure of galaxies at redshift 4.1.
