Overview of the Rosette Nebula on a Berschel SPIRE 250 µm surface brightness map. The cores observed at Effelsberg are shown with different colours, which indicate their evolutionary stages derived from Berschel data by Motte et al. (2010): (green) warm-starless, (blue) prestellar, (red) protostellar core. The yellow dots represent the stars of the cluster NGC 2244. The white and purple stars mark the O and B stars of the cluster, respectively. The areas indicated by black rectangles and the YSO clusters indicated by yellow circles are presented in Sect. 1. The inserts give a closer look at areas PL03, Shell, Center, and AFGL 961 in order to clearly distinguish our sources.