This document describes the Po-tree, a new indexing structure for spatio-temporal databases with soft real-time constraints. Natural risks management and other system can use arrays of spatially referenced sensors. Each on them sending their measurements to a central database. Our solution tries to facilitate the indexing of these data, while favoring the newer ones. It does so by combining two sub-structures for the spatial and temporal components. While Mobility is not yet supported, evolutions of the structures shall be able to deal with it