The use of modern large telescopes makes it possible to observe and study the formation and evolution of clusters of galaxies. We used the Lyman break technique to identify ~900 candidate high-redshift galaxies in a wide field surrounding radio galaxy TN J1338-1942. This massive galaxy, located at a redshift z = 4.1 is known to be surrounded by a spatial overdensity of galaxies detected by their strong Lyman-alpha lines. The use of the Lyman break technique enabled us to study the distribution of galaxies by higher numbers and to larger extend. In this lunchtalk I will present the results of this study, which includes additional evidence for the presence of a proto-cluster around TN J1338-1942 as well as an analysis of the high-redshift galaxy distribution at larger scales.