We address the question as to which are the minimal ingredients to obtain a decentralised gathering of agents that move on a lattice. The agents and their environment are described with a stochastic model inspired from biology: the aggregation of the {\em Dictyostelium discoideum} cellular slime mold. The environment is an active lattice, which cells transmit information according to a reaction-diffusion mechanism. The agents trigger excitations randomly; they move by following excitation fronts. We show that despite its simplicity this model exhibits interesting properties of self-organisation and allows to achieve decentralised gathering. Moreover, observations show that the system has interesting robustness properties, as being able to resist to the presence of obstacles on the lattice and to resist to the addition of noise on the moves on the agents.