  The Trifid nebula is a young HII region undergoing a burst of star formation.
In this article, we report on far-infrared and millimeter continuum and line
observations of several massive and bright protostellar sources in the vicinity
of the exciting star fo the nebula, just behind the ionization front. These
objects are probably young protostars (Class 0) and are associated with very
massive cores (M ~ 8-90 Msol) powering young energetic outflows. Analysis of
the far-infrared emission in the 45-200 micron range from ISO/LWS data shows
that they are embedded in cold dense material. Inspection of their physical
properties suggest that they are similar to the dust protostellar cores
observed in Orion, although at an earlier evolutionary "Pre-Orion" stage. The
cores are embedded in a compressed layer of dense gas. Based on comparison with
the models, we find that the cores could have formed from the fragmentation of
the layer and that the birth of the protostars was triggered by the expansion
of the Trifid nebula.
