Bacteria are among the most common and resilient forms of life on Earth, and their extraordinary surface-colonizing ability represents a central topic in microbiology, biophysics, and materials science. This process typically starts with few cells undergoing a phenotypical switch from the plantonik (i.e. swimming) to the sessile (i.e. surface-associated) lifestyle and continue via the formation of an exponentially growing monolayer of tightly packed and partially ordered cells. Colonies originating from a single bacterium, initially develops in the form of a flat and circularly symmetric monolayer and, after reaching a critical population, invade the three-dimensional space forming stacks of concentric disk-shaped layers. In this talk I will discuss some recent theoretical progress toward understanding the geometry of bacterial monolayers as well as the statistical mechanics underpinning the mono-to-multilayer transition.