The MOnolithic Stitched Sensor (MOSS) is a development prototype chip towards the ITS3 vertexing detector for the ALICE experiment at the LHC. Designed using a 65 nm CMOS Imaging technology, it aims at profiting from the stitching technique to construct a single-die monolithic pixel detector of 1.4 cm x 26 cm. The MOSS prototype is one of the prototypes developed within the CERN-EP R , D framework to learn how to make stitched wafer-scale sensors with satisfactory yield. This contribution will describe some of the design challenges of a stitched pixel sensor , the techniques adopted during the development of this prototype.