Minecraft wiki entry for Defense, associated text: A lava-filled moat, on the other hand, will kill any mobs in short order by itself, but also destroy any drops. Lava-moats have the additional benefit of producing light, stopping mobs from spawning nearby without torches. However, it can be laborious to collect large quantities of lava, which requires at minimum buckets and the discovery of a sizable source of lava. Structures over a lava moat (bridges, overhanging walls, etc.) should have fences or a raised edge to stop players from falling or being knocked in. Lava should not be used where there are flammable blocks nearby, especially trees, planks blocks, or wool (among others).